vvEPA
         United States
         Environmental Protection
         Agency
          Industrial Environmental Research
          Laboratory
          Research Triangle Park IMC 27711
EPA-600/9-80-004
January 1980
Proceedings:
Advances in Particle
Sampling and
Measurement
(Daytona Beach,  FL,
October 1979)
                   rivironment
                    ram Report

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                 RESEARCH REPORTING SERIES


Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology.  Elimination  of  traditional  grouping  was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:

    1. Environmental Health Effects Research

    2. Environmental Protection Technology

    3. Ecological Research

    4. Environmental Monitoring

    5. Socioeconomic Environmental Studies

    6. Scientific and Technical Assessment Reports  (STAR)

    7. Interagency Energy-Environment Research and Development

    8. "Special" Reports

    9. Miscellaneous Reports

This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND  DEVELOPMENT series. Reports m this series  result from the
effort funded  under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects;  assessments of, and development of, control technologies for energy
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mental issues.
                       EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
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This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

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                                  EPA-600/9-80-004

                                        January 1980
               Proceedings:
   Advances in  Particle  Sampling
           and  Measurement
(Daytona  Beach, FL, October  1979)
                W.B. Smith, Editor

              Southern Research Institute
              2000 Ninth Avenue, South
             Birmingham, Alabama 35205
              Contract No. 68-02-3118
             Program Element No. EHE624
           EPA Project Officer: D. Bruce Harris

         Industrial Environmental Research Laboratory
       Office of Environmental Engineering and Technology
            Research Triangle Park, NC 2771 1
                  Prepared for

        U.S. ENVIRONMENTAL PROTECTION AGENCY
           Office of Research and Development
               Washington, DC 20460

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                              PREFACE
     The symposium was sponsored by the Process Measurements
Branch, Industrial Environmental Research Laboratory, U.S. En-
vironmental Protection Agency.  D. Bruce Harris, EPA, served
as chairman.  Session chairmen were Robert Carr (Electric Power
Research Institute), W.B. Kuykendal (EPA), Benjamin Y.H. Liu
(University of Minnesota), Otto Raabe  (University of California-
Davis) , and Herbert Spencer, III  (Joy Manufacturing Co.).  A.B.
Craig, Director of the Industrial Processes Division of EPA,
delivered a welcoming address.

     A list of reports on the research supported by the Process
Measurements Branch can be obtained from Mrs. Judy Ford, MD-62,
Process Measurements Branch, Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, Research Triangle
Park, NC 27711.
                               111

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                           CONTENTS
Preface	iii
Speakers and Chairmen 	 vii

Paper 1.  An Experimental Study of Virtual Impactors
Thomas J. Yule and Christopher G. Broniarek	   1
Paper 2.  A Theoretical Study of Virtual Impactors
Virgil A. Marple and Chung M. Chien	22

Paper 3.  A Heavy Grain-Loading Impactor
Dale A. Lundgren, Ernest R. Cerini and Michael L. Smith 	  54

Paper 4.  Velocimetric Determination of Aerodynamic Diameter
  in the Range from 0.1 ym to 15 pm
James C. Wilson and Benjamin Y.H.  Liu	67

Paper 5.  A Prototype Particulate Stack Sampler with Single-Cut
  Nozzle and Microcomputer Calculating/Display System
John C. Elder, Larry G. Littlefield, and Marvin I. Tillery. ...  83

Paper 6.  The Effects of Nozzle Losses on Impactor Sampling
Kenneth T. Knapp	101

Paper 7.  Dilution Source Sampling System
Robert J. Heinsohn, John W. Davis, and Kenneth T. Knapp 	 107

Paper 8.  Aerosol Characterization with a Quartz Crystal
  Microbalance Cascade Impactor
David C. Woods and Raymond L. Chuan	130

Paper 9.  Extending Precision in a Computer-Based Cascade
  Impactor Data Reduction System
Jean W. Johnson, B. E. Pyle, and Wallace B. Smith	146

Paper 10. Implementing CIDRS - A Programmer's Perspective
Clinton E. Tatsch	167

Paper 11. Numerical Simulation Studies and Data Reduction
  for Size Classifying Measurement Techniques
H. Fissan and C. Helsper	180

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Paper 12.  Non-Ideal Behavior in Cascade Impactors
Joseph D. McCain and James E. McCormack	201

Paper 13.  Field Testing of Automatic Piezoelectric Microbalances
  for Outdoor Aerosol Mass Concentration Measurements
Kazuo Tsurubayashi and Hajime Kano	217

Paper 14.  A New Real-Time Isokinetic Dust Mass Monitoring System
James C.F. Wang	242

Paper 15.  A New Real-Time Mass Monitoring Instrument:  The TEOM
Harvey Patashnick and Georg Rupprecht	264

Paper 16.  New Automated Diffusion Battery/Condensation Nucleus
  Counter Submicron Sizing System:  Description and Comparison
  with an Electrical Aerosol Analyzer
Gilmore J. Sem, Jugal K. Agarwal, and Charles E. McManus 	 276

Paper 17.  An In-Situ Liquid Droplet Sizing System
Daniel E. Magnus and David S. Mahler	302

Paper 18.  Some Aerodynamic Methods for Sampling Inhalable
  Particles
Wallace B. Smith, Kenneth M. Gushing, M.  Christine Thomas,
  and Rufus R. Wilson, Jr	316

Paper 19.  Deposition of Inhaled Particles and Possible
  Sampling Methods
Vittorio Prodi, Giuseppe Tarroni, and Carlo Melandri 	 348

Paper 20.  Aerosol Sampling Inlets and Inhalable Particles
Benjamin Y.H.  Liu and David Y.H. Pui	382
                                VI

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                      SPEAKERS AND CHAIRMEN
Robert Carr
Electric Power Research Institute
P.O. Box 10402
Palo Alto, CA 94304
Phone:  415/855-2422 ext. 137

Raymond L. Chuan
Defense Division
Brunswick Corporation
3333 Harbor Boulevard
Costa Mesa, CA 92626
Phone:  714/546-8030

A.B. Craig
Director, Industrial Processes
  Division
Environmental Protection
  Agency
Research Triangle Park, NC 27711

Dennis Drehmel
Environmental Protection Agency
Particulate Technology Branch
Utilities & Industrial Power
  Division
Research Triangle Park, NC 27711

John C. Elder
Aerosol Studies Section
Industrial Hygiene Group
University of California
Los Alamos Scientific Laboratory
P.O. Box 1663
Los Alamos, NM 87545

H. Fissan
Gesamthochschule Duisburg
Aerosolmesstechnik
4100 Duisburg
Bismarckstrasse, 81
Federal Republic of Germany
Phone:  0203 392 202

D. Bruce Harris
Environmental Protection Agency
Industrial Environmental Re-
  search Laboratory
Mail Stop MD-62
Research Triangle Park, NC 27711
Phone:  919/541-2557
Robert J. Heinsohn
Pennsylvania State University
Mechanical Engineering Department
University Park, PA 16802
Phone:  814/865-8281

Jean W. Johnson
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, AL 35205
Phone:  205/323-6592 ext. 547

Kenneth T. Knapp
Particulate Emissions Research
  Section
Environmental Sciences Research
  Laboratory
Environmental Protection Agency
Environmental Research Center
Mail Stop MD-46
Research Triangle Park, NC 27711
Phone:  919/541-3085

W.B. Kuykendal
Environmental Protection Agency
Industrial Environmental Re-
  search Laboratory
Mail Stop MD-62
Research Triangle Park, NC 27711
Phone:  919/541-2557

Benjamin Y.H. Liu
University of Minnesota
Department of Mechanical
  Engineering
125 Mechanical Engineering
111 Church Street S.E.
Minneapolis, MN 55455
Phone:  612/373-3043

Dale A. Lundgren
University of Florida
Department of Environmental
  Engineering Sciences
A.P. Black Hall
Gainesville, FL 32611
Phone:  904/392-0846
                              VII

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Dan Magnus
KLD Associates, Inc.
300 Broadway
Huntington Station, NY 11746
Phone:  561/549-9803

Virgil A. Marple
University of Minnesota
Mechanical Engineering Department
111 Church Street_S.E.
Minneapolis, MN 55455
Phone:  612/373-9984

Joseph D. McCain
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, AL 35205
Phone:  205/323-6952 ext. 278

Harvey Patashnick
Rupprecht and Patashnick Company
255 Hackett Boulevard
Albany, NY 12208
Phone:  518/438-5569

Vittorio Prodi
Comitato Nazionale per L'Energia
  Nucleare
Centro di Calcolo
Laboratorio Fisica Sanitaria
Bologna
Via Massini, 2 - Cap 40138
Italy

Otto Raabe
Laboratory of Radiobiology
University of California - Davis
Davis, CA 95616
Phone:  916/752-7754

Gilmore Sem
TSI Incorporated
500 Cardigan Road
P.O. Box 3394
St. Paul, MN 55165
Phone:  612/483-0900

Wallace B. Smith
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, AL 35205
Phone:  205/323-6592 ext. 520
Herbert Spencer, III
Western Precipitators Division
Joy Manufacturing Company
565 Colorado Boulevard
P.O. Box 2744, Terminal Annex
Los Angeles, CA 90051
Phone:  213/240-2300

C.E. Tatsch
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, NC 27709
Phone:  919/541-6000

Kazuo Tsurubayashi
Nihon Kagaku Kogyo Co., Ltd.
Head Office, 2-1
Shimizu, Suita
Osaka
Japan

James C.F. Wang
Combustion Research Division
Sandia Laboratories
Livermore, CA 94550

James C. Wilson
University of Minnesota
Department of Mechanical
  Engineering
125 Mechanical Engineering
111 Church Street S.E.
Minneapolis, MN 55455
Phone:  612/373-9984

David C. Woods
NASA Langley Research Center
Hampton, VA 23665

Thomas J. Yule
Applied Physics Division
Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439
Phone:  312/739-7711
                             vixi

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                              PAPER 1
            AN EXPERIMENTAL STUDY OF VIRTUAL IMPACTORS
                          THOMAS J. YULE
                    ARGONNE  NATIONAL LABORATORY

                                AND

                     CHRISTOPHER G. BRONIAREK
                 RENSSELAER POLYTECHNIC INSTITUTE
ABSTRACT
     Virtual impactors are currently being used in a number of
instruments to separate an aerosol into different size ranges.
The virtual impactor is a variation of the standard impactor
in which the impaction surface is replaced by an orifice into
which particles can pass and be collected or counted.  We have
made an experimental study of the collection characteristics
of virtual impactors.  The parameters varied included: accelera-
tion nozzle-to-collection probe distance, the ratio of the collec-
tion probe-to-acceleration nozzle diameters, and the ratio of
collection probe-to-inlet flows.  Measurements were also made
with different collection probe geometries.  It was found that
it is possible to parameterize much of the data by introduction
of the Stokes number and an effective minor flow collection ef-
ficiency.  One disadvantage of the virtual impactor is that in
the transition region particles are collected on the inside walls
of the collection probe near the probe tip.  The amount that
is collected is a sensitive function of the probe geometry.

INTRODUCTION

     Virtual impactors are currently being used in a number of
instruments to separate an aerosol into different size ranges.
The virtual impactor is a variation of the standard impactor
in which the impaction surface is replaced by a collection probe
into which large particles will pass and then be collected or
counted.  Figure 1 is a schematic illustrating the operation
of a virtual impactor.   The aerosol stream is drawn through the
acceleration nozzle where the velocity of the particles is in-
creased.  A collection probe is located at a short distance below

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         STREAMLINES
   TRAJECTORY OF
   PARTICLE TOO
   SMALL TO IMPACT
                                                        ACCELERATION
                                                        NOZZLE
/
f
/
/
/
/
/
/
y
W
\ \ i *

QI
(1
1





« DT ••

^ 	 TRA-IFHTORV OP
\
/
r.
f
/
/
/
/
V.
IMPACTED PARTICLE



	 COLLECTION
-^""^ PROBE



Figure 1.  Schematic view of a virtual impactor showing representative streamlines
         and particle trajectories.

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the acceleration nozzle.  Flow conditions are maintained such
that the flow in the collection probe is a fixed fraction of
the inlet flow.  A few representative streamlines are shown on
the figure.

     In order to understand the principle of operation/ consider
particles that exit from the acceleration nozzle near streamlines
which do not pass through the collection probe.  Small particles
follow the streamlines and remain in the flow that does not pass
through the collection probe; large particles are unable to fol-
low the streamlines in regions of rapidly changing curvature
and become caught up in the flow that passes through the collec-
tion probe.  The flow in the collection probe, Qj, is referred
to as the minor flow.  The ratio Qi/Q<>f where Q0 is the inlet
flow, ranges in value from 0.03 to 0.25 in present designs.
For zero particle size a fraction of the particles equal to Qi/Q0
follow the streamlines of the minor flow and pass through the
collection probe.  The small particles that enter the collection
probe along with the large particles introduce cross contami-
nation.  The flow which does not enter the collection probe is
referred to as the major flow; it contains most of the small
particles.

     Virtual impactors possess a number of advantages over stand-
ard impactors.  These are: the size and placement of the size-
separated sample can be optimized for the analysis system, par-
ticle bounce and reentrainment are minimized, and significant
amounts of a sample can be collected without serious loading
problems and without change in collection efficiency.  There
are also disadvantages.  These are: the slope of the efficiency
curve is less steep than that for a well-designed standard im-
pactor, there is always some cross contamination, and some of
the sample is collected on the inside walls of the collection
probe.

     The method of virtual impaction was introduced by Hounam
and Sherwood1 in 1965.  They designed and constructed a multi-
stage device called a cascade centripeter, which had cutpoints
of 1.2, 3.5, and 12 micrometers.  Flat orifice plates were used
instead of acceleration nozzles.  Their device had considerable
wall losses.  Shortly afterward, Conner2 investigated the col-
lection efficiency of a single-stage virtual impactor as a func-
tion of operating parameters.

     More recently, interest in virtual impactors has been height
tened by the U.S. Environmental Protection Agency's desire for
a device which collects size-segregated ambient aerosol samples
for large-scale monitoring applications.  The device, which is
referred to as a dichotomous sampler, separately collects fine
(<2.5 micrometer) and coarse (>2.5 micrometer) airborne particles.
An early design, which has two stages, is described by Dzubay
and Stevens3 and Loo, et al.1*  A second generation sampler, which

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has only a single stage and very low internal losses, has been
developed by Loo, et al.5  Virtual impactors have also appeared
in other devices.  McFarland, et al.6 have developed a sampler
that was used to collect large quantities of particulate matter
from the stack of a coal-fired power plant.  Kotrappa, et al.7
and Yule8 have used virtual impactors to size segregate radio-
active aerosols in radiation detection instruments.

     To aid in the development of the devices described above,
various experimental studies on virtual impactors were under-
taken.  The most extensive studies are those by Loo, et al.4
and by McFarland, et al.9  Both studies were aimed at determining
the optimum parameters for attaining sharp cutoffs with minimum
internal losses for particular systems.  The study reported here
is somewhat broader in scope.  It was undertaken to provide suf-
ficient information to determine the cutoff size and collection
characteristics for a wide range of system parameters.  The study
was patterned after the study on standard  impactors by Marple
and Liu.10

     There have also been some theoretical studies of virtual
impactors by Marple and Chien11 and by Hassan, et al.12  In gen-
eral, these studies have given insight into the separation charac-
teristics, but the agreement between measured and predicted data
is not as good as that for the standard impactor.

EXPERIMENTAL METHODS

     The collection characteristics of virtual impactors were
studied using monodisperse aerosols.  Most of the measurements
were made with dioctyl phthalate  (DOP) droplets, which contained
trace amounts of uranine  (the sodium salt  of fluorescein) dye
as a tracer.  Aerosols with sizes from 1 to 10 micrometers were
generated with a Berglund-Liu vibrating-orif ice aerosol gener-
ator.   Some measurements  were also  made with polystyrene  latex
(PSL) aerosols.  The PSL  aerosol generator consisted of a nebu-
lizer, diluter, diffusion dryer, and Kr-85 charge neutralizer.
The collection characteristics for  the two aerosols  are expected
to be different since one is a liquid droplet which  will stick
on contacting a surface,  while the  other  is an elastic  sphere
which can rebound from a  surface.   The results obtained with
the DOP aerosols represent an upper  limit  for collection on
surfaces of the virtual  impactor and are easier to  compare with
calculated results, because one can  assume any droplet  that comes
in contact with a surface will stick to that surface.

     Figure 2 is a schematic view of the single-stage virtual-
impactor test assembly that was used for the measurements.  The
assembly allows one to easily change the acceleration nozzle
and collection probe geometries.  For measurements  with the DOP
aerosols the quality of  the aerosols was monitored  with an op-
tical particle counter that had the  probe  located  in a  region

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               till I,<
    MAJOR
    FLOW
               r r { / r r

                                       \
                                     MINOR
                                     FLOW
Figure 2. Apparatus for measuring the collection characteristics of virtual impactors.
         Some of the key components are indicated:  1.  acceleration nozzle, 2.  flow
         transition cone, and 3.  collection probe.

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above the inlet.  A Bausch and Lomb 40-lA counter was used with
a modified flow system, as described by Marple, et al.,13 and
with interface electronics that allows pulse-height analysis
with a multichannel analyzer.  Such a monitor is very useful
in determining whether the aerosol generator is operating properly.
For the measurements with OOP aerosols filters were inserted
in the minor and major flow lines.  Flow measurements were made
with pressure-corrected rotameters.  Measurement times were on
the order of 15 minutes.  The aerosol depositions were deter-
mined on various comp'onents: the underside of the piece support-
ing the acceleration nozzle, the acceleration nozzle, the collec-
tion probe, and the major and minor flow filters.  These are
the only areas where there are significant deposits.  The de-
posits were determined by washing the pieces or filters in mea-
sured amounts of a buffer solution  (0.05 M Na.HPO^) and using
fluorescence techniques.  A Turner Model 110 rluorometer was
used; calibration curves had been determined which relate the
absorption to the uranine concentration.  Concentrations as low
as 0.005 yg/ml can be reliably determined.

     For measurements with the PSL aerosols two aerosol sizes
were used:  1.10 and 2.02 micrometers.  The optical particle coun-
ter probe was placed in a region below the collection probe.
For these measurements only the fraction of the incoming aerosol
that passed through the collection probe was determined.  For
a given particle size and flow conditions, the aerosol concentra-
tions before and after each measurement were determined by set-
ting the major flow, Q2, equal to zero and Q0 equal to the nominal
value of Qj.  The average concentration, Cg =g, was determined.
With the nominal values of Q0 and Q2 established, the concentra-
tion, C, in the minor flow was measured.  The minor flow collec-
tion efficiency, Em, is simply
                            _
               "m    (Qo/Qi) CQz=0  '

RESULTS AND DISCUSSION

     A series of measurements were made with OOP aerosols  in
which various geometrical and flow conditions were varied.  A
virtual impactor with geometrical and flow parameters  listed
in Table 1 was chosen as a standard; individual parameters  were
varied about these values.  A value of DJ/DQ = 1.28 was  chosen
for the standard, because this value results in minimum  wall
losses in the collection probe.  The shape of the collection
probe is the same as that shown  in Figure 1.  As is discussed
below, this shape is not the optimum shape for minimum collec-
tion on the interior walls of the collection probe; however,
it is a shape that has been used in a number of devices  and is
easy to treat analytically.  Figure 3 shows the collection  charac
teristics for the standard.  Since the deposits in the accelera-
tion nozzle and on the underside of the piece supporting the

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1.2
1.0  —
I I I I
MAJOR FLOW
/"""
I I I I I

Q^QQ = 0.25
Re = 10.000 _
                                     MINOR FLOW
                                   COLLECTION PROBE
                                         I
                   I
345

    PARTICLE DIAMETER,
                                                                          S/D0 = 1.0
                                                                                1.28
                                                                                                  10
                 Figure 3.  Collection efficiencies for the standard virtual impactor.

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           TABLE  1.   GEOMETRICAL  AND  FLOW PARAMETERS  FOR THE
                       STANDARD VIRTUAL  IMPACTOR

Parameter
Do
D!/DO
S/DO
T/DO
Qo
Qi/Qo
Value
3.912 mm
1.28
1.0
2.0
27.7 S,/mina
0.25

            Corresponds  to a  jet  Reynolds  number  of  10,000.
acceleration nozzle were very small, they are not shown.  The
minor flow collection efficiency is 0.25, which is simply the
ratio QJ/QQ, for small particle sizes and reaches a value of
1.00 for large particle sizes.  The region in which the minor
flow collection efficiency is varying is referred to as the
transition region.  It is useful to define an effective minor
flow collection efficiency, E_,

                         Em ~ Ql/Qo
                    Em = 1 - (h/Qo  '                          (2)


which corresponds  to  the efficiency for  removing particles  from
the major flow and having them pass through  the collection  probe.
Em may assume values  from zero to  unity.  We choose to  define
the cutoff  for a virtual impactor  as that size for which  E^ =  0.5,
Note that it is only  in the transition region that there  is signi-
ficant collection  on  the walls of  the collection probe. For the
standard the maximum  value is approximately  0.20.  For  aerosols
that have a probability of rebounding from contact with a wall,
this maximum is reduced.  In order  to investigate the wall  losses
in the collection  probe in more detail,  a special collection
probe, shown in Figure 4, was constructed.   The thickness of
the annular inserts was one-third  D0.  Measurements were  made
with 2,  2.5, and  3 micrometer DOP  aerosols.  For all sizes  close
to 100%  of  the deposit appeared on the inside of the top  ring.
This result indicates that the shape of  the  collection  probe
could significantly influence the  magnitude  of the wall losses
in the transition  region.

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                                                    10 mm
              Figure 4. Modified collection probe with annular inserts.


     For standard impactors  it  has  been found useful to show
the characteristic impaction curves with the abscissa expressed
in units of the square root  of  the  Stokes  number, /St,  which
is a dimensionless particle  size.10  The Stokes  number, as de-
fined by Fuchs,11* is  the ratio  of the particle stopping distance
to the radius of the  impactor throat,
                    St  =
pp C Vo Dp
    Do/2
(3)
where pp is the particle density,  C is  the Cunningham slip cor-
rection factor, V0  is  the mean  velocity in the throat, Dp is
the particle diameter, y is  the fluid viscosity, and D0 is the
diameter of the throat.  When plotted in this fashion, it has
been found that the  impaction curves are only slowly varying
functions of S/D, the  Reynolds  number,  and T/D.   (See Figure 1
for definitions of  S and T.)  A similar representation is useful
for showing the collection curves_for virtual impactors.  Fig-
ure 5 shows Em as a  function of /St for measurements for which
QI/QO' S/D0, DJ/DO,  and T/D0 were  held  constant  and D0, Dp, and
Qo were varied.  Two values  of  D0  were  used;  0.3048 and the
standard 0.3912 cm.  For a particular data set either Q0 was

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                                OT
                          COLLECTION EFFICIENCY
                   p
                   to
                             p
                             b>
p
bo
4.
o o
 «;
r* a?
L- ^3>
?»§!
SIS*
     I
           p
           w
           p
           ui
           p
           en
           p
           bo
           p
           to

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varied and Dp kept constant, or Dp was varied and Q0 kept con-
stant.  For the former, this corresponds to a variation in Rey-
nolds number, Re, of a factor of four.  In general, all the data
for DO = 0.3048 cm fall on a single curve, while those for D0
= 0.3912 cm lie slightly above the curve.  This small variation
is almost entirely due to different finishes on the inside walls
of the collection probes.  The inside wall of the larger probe
was polished and had a maximum collection of 0.20, whereas the
other one had a rougher surface and had a maximum collection
of 0.25.  A typical collection curve for a standard impactor
is also shown on the figure; it is significantly steeper.

     The collection characteristics of virtual impactors as a
function of S/D0, D!/DO, and Qi/Qo were determined.  The varia-
tion with T/Do was not determined.  The analytical studies indi-
cate that it should be small for T/D0 values greater than one-
half.  Studies were not made of the variation in collection
characteristics for wide ranges of Reynolds numbers, since the
analytical studies indicate that to see a significant deviation,
it would be necessary to go to very low values of the Reynolds
number.  Such measurements would have been quite interesting,
but would have required a complete redesign of the experimental
apparatus.  Figure 6 shows the variation in the collection charac-
teristics for 2-micrometer size particles as a function of S/D0,
with all other parameters fixed at those of the standard.  This
variation with S/D0 is significantly greater than that seen for
a standard impactor and is related to the divergence of the jet
as S/Do increases.  Figure 7 shows the variation in the collec-
tion characteristics for 2 and 10-micrometer size particles as
a function of DJ/DQ.  For the 2-micrometer size particles the
collection on the walls of the probe significantly increases
for DI/DO greater than 1.6.  Studies by Loo, et al.1* with solid
particles show similar results and also indicate that a mini-
mum occurs at about D!/DO = 1.3.  For the 10-micrometer size
particles increased wall losses in the collection probe begin
at DI/DO greater than 1.4.

     The ratio Qi/Qo was also varied.  Figure 8 shows the results
for Qi/Qo = 0.10.  The transition region is moved to larger par-
ticle sizes.  The peak of the collection-probe wall-losses curve
stays at around 0.20.  There is also a small amount collected
on the underside of the acceleration nozzle and on the accelera-
tion nozzle support structure.  Figure 9 shows the results for
Qi/Qo = 0.03.  The transition region is moved to even larger
particle sizes.  The peak of the collection-probe wall-losses
curve increases to about 0.30.  In order to parameterize these
results it is convenient to use the effective minor flow collec-
tion efficiency, Em, which was previously defined.  Figure 10
shows Em versus /St for various values of QJ/QQ.   It is seen
that over a significant portion of the transition region the
                               11

-------
    1.0
    0.8
UJ


£   0.6
Z
o

O   0.4
8
    0.2
  COLLECTION
' PROBE

       O
                                                    S/DO
                Figure 6.  Variation in the collection efficiencies for 2-micrometer size particles

                         as a function of S/Drj.

-------
                                            COLLECTION EFFICIENCY
  f
  N

l.|

ft
    .


1
I
•**

I

I
   I'
        o
       o
                                                                            p

                                                                            b>
                                                                                    p

                                                                                    bo
                                                                                             fi-


                                                                                             ts)
                                                           .
                                                                             D




                                                                            D




                                                                            D
                                                                  a o
                                                                                        r-  o  O
                                                                                        m  3,  3,

                                                                                        H  TI  ~n



                                                                                        HI
                                                                                        •o
                                                                                        3D

                                                                                        O
                                                                                        00
                                                                                        m

-------
                                    frT
                           COLLECTION EFFICIENCY
  f
  Po
§
3 *
ft\ ^h
 . 03
  *
s?
  CB
  I
•o
>
31

O
|-
m

O

>

m
      T=
          •>i  —
          00  —
    co —

-------
>
o
ui



O


o
ui
O
o
INLET PLUS

INLET SUPPORT
    0.2  -
                                          456




                                         PARTICLE DIAMETER, ju
                                     10
              Figure 9.  Collection efficiencies for a virtual impactor for which all the parameters

                       are the same as those for the standard except Q//Q0 = 0.03.

-------
     1.0
     0.8
     0.6
     0.4
     I 0.2
                Q.J/QQ = 0.25
              J_
                                                 0.03
                                             I
        0      0.2     0.4    0.6     0.8     1.0     1.2     1.4     1.6     1.8

                                    \/St~

      Figure 10.  Effective minor flow collection efficiencies for various values of
data is fitted  by  a straightJJ.ne.  The line may  be  characterized
by specifying the  value of /St at E^ = 0.50 and  the  rate of
change of the line,  R,  which is defined as
                          . 0.80
                          = 0.20
R =
                          /St
                                                                (4)
                             E' = 0.50
                              m
where the subscript on /5t indicates the value  of E^.   Figure 11
shows the variation of •/St'Em = 0.50 versus Qi/Qo.  R remained
constant at  a  value of 0.65.

     In addition  to the measurements described  above,  a number
of measurements were made to determine the effect of changing
the shape of the  collection probe.  Figure 12 shows two different
shapes of collection probes that were used:  a  disc with a hole
in it and a  tube  with rounded inside edges.  The  collection
characteristics for the disc were identical with  those for the
standard.  The collection characteristics for the tube with
rounded inside edges were significantly different.   The collec-
tion-probe wall-losses curve had approximately  the same shape
as that for  the standard, but the magnitude was decreased by
about 35%.   There was a corresponding change in the collection
curve for the  major flow, while the collection  curve for the
                                16

-------
     1.25
  «  1.00 -
  o
  ii
  E
(.
         0.00
                                                                               0.30
     Figure 11.  The variation in  ^/St at which the effective minor flow collection
                 efficiency is 0.50 as a function of
E
                            //
                                             k/vJ
//
                         (a) DISC WITH A HOLE THROUGH IT
                        (b) TUBE WITH ROUNDED INSIDE EDGES
                        Figure  12.  Modified collection probes.
                                        17

-------
minor flow remained unchanged.  This result indicates that by
rounding the inside edges of the collection probe particles that
would have been deposited near the top are now able to remain
in the major flow.  Loo and Cork15 have optimized the geometrical
parameters for a particular design and have been able to reduce
the losses for liquid particles to less than 1% for all particle
sizes up to 20 micrometers.

     Measurements were also made of the minor flow collection
efficiency with PSL aerosols.  The results are shown in Figure
13.  Also shown on the figure are the curves for minor flow and
receiving tube collection with OOP aerosols.  Note that the
results are quite similar for values of /S~E less than 0.5, but
that the OOP values are lower than the PSL values over the range
from 0.5 to 0.9.  The differences are explained by the fact that
a droplet on striking a wall will stick, whereas a PSL sphere
has a certain probability for rebounding.  Apparently, the spheres
that rebound from the walls can either enter the minor flow or
be swept out of the tube in the major flow.  The former appears
to be much more likely for spheres with values of /St near 0.8,
the latter for those with values less than 0.5.  Loo, et al.1*
found that with solid aerosols of uranine the maximum collection
in the receiving tube with this geometry was only a few percent.

CONCLUSIONS

     The purpose of this study was twofold: 1) to provide data
that is useful in designing systems which employ virtual impac-
tors, and 2) to develop an improved understanding of the prin-
ciples of operation of virtual impactors.  It was found that
it is possible to parameterize much of the data by the introduc-
tion of the Stokes number and an effective minor flow collection
efficiency.  For given Q1/QOI DJ/DQ, and S/D0, there is a single
curve which represents the minor flow collection efficiency as
a function of /St.  Analytical studies indicate that the curve
should apply to quite low values of_Reynolds number.11  For dif-
ferent values of Ch/Qo/ Eff, versus /St is rather well represented
by a straight line whose rate of change stays constant and for
which /St Em = o.50 ^s a smoothly decreasing function of Qi/Q0.
Thus, Figures 10 and 11 can be used to determine effective minor
flow collection efficiency curves for a wide range of system
parameters.  The study also indicated that the collection ef-
ficiencies for virtual impactors are more dependent on S/D0 for
values greater than one, than the collection efficiency for a
standard impactor.

     One disadvantage of the virtual impactor is that in the
transition region particles are collected on the inside walls
of the collection probe near the probe tip.  It was found in
this study and in the study by Loo, et al.4 that this collection
is minimized if Dj/D,, is kept at a value of about 1.3.  Further-
more, the amount that is collected is a sensitive function of
                               18

-------
                                  6T
                             COLLECTION EFFICIENCY
  f-o
II Q
-* O'
II
5
II
"I
   ii
            p
            b
              p
              b
          p
          to
                                      p
                                      b>
p
oo
            p
            ro
p
bo
                                               * Od*
                                               10 CO CO bO
                                                o
                                             O
                                             O

                                             3
                                             a
                                             •o

-------
 the  probe geometry.   Rounding  the inside of the probe tip,  polish-
 ing  this  surface,  and maintaining good alignment between the
 acceleration nozzle  and collection probe minimizes  the amount
 collected.   Using  trial-and-error methods,  Loo and  Cork15 have
 been able to minimize the collection peak to less than 1% for
 a particular set of  flow and geometry conditions.  At this  time
 it is not known whether such dramatic improvements  are possible
 for  arbitrary flow conditions.

 ACKNOWLEDGEMENT

      This research was performed under the auspices of the U.S.
 Department of Energy.  The submitted manuscript has been authored
 by a contractor of the U.S.  Government under contract No. W-31-
 109-ENG-38.  Accordingly, the  U.S. Government retains a non-
 exclusive, royalty-free license to publish or reproduce the pub-
 lished form of this  contribution, or allow others to do so, for
 U.S. Government purposes.

REFERENCES

 1.  Hounam, R.F.,  and R.J. Sherwood.  The Cascade Centripeter:
     A Device for Determining the Concentration and Size Distri-
     bution of Aerosols.  Am.  Ind. Hyg. J. 26:122-131, 1965.

 2.  Conner, W.D.  An Inertial-Type Particle Separator for Col-
     lecting Large Samples.  J. Air Pollut. Control Assoc. 16(1):35-
     38, 1966.

 3.  Dzubay, T.G.,  and R.K. Stevens.  Ambient Air Analysis with
     Dichotomous Sampler and X-Ray Fluorescence Spectrometer.
     Environ. Sci.  Technol. 9(7):663-668, 1975.

 4.  Loo,  B.W., J.M.  Jaklevic,  and F.S. Goulding.  Dichotomous
     Virtual Impactors  for Large-Scale Monitoring of Airborne
     Particulate Matter.  In:  Fine Particles: Aerosol Generation,
     Measurement, Sampling, and  Analysis, B.Y.H.  Liu,  ed.  Academic
     Press, New York, 1976.  pp.  311-350.

 5.  Loo,  B.W., R.S.  Adachi, C.P.  Cork, F.S. Goulding, J.M.  Jaklevic,
     D.A.  Landis, and W.L. Searles.   A Second Generation  Dichotomous
     Sampler for Large-Scale Monitoring of Airborne Particulate
     Matter.   Lawrence  Berkeley  Laboratory Report LBL-8725,  1979.

 6.  McFarland, A.R., R.W. Bertch, G.L. Fisher,  and B.A.  Prentice.
     Fractionator for Size Classification of Aerosolized  Solid
     Particulate Matter.  Environ.  Sci. Technol.  11(8):781-784,
      1977.

 7.  Kotrappa,  P., D.P.  Bhanti,  S.K.  Dua, and  P.P.  Joshi.  A
     Single  Stage Centripeter  for  Rapid Analysis  of Long-Lived
     Alpha  Emitters  in  Air.  Health  Phys. 27:103-108,  1974.
                                20

-------
 8.  Yule, T.J.  An On-Line Monitor for Alpha-Emitting Aerosols.
     IEEE Trans. Nucl. Sci. NS-25(1):762-766, 1978.

 9.  McFarland, A.R., C.A. Ortiz, and R.W. Bertch, Jr.  Particle
     Collection Characteristics of a Single-stage Dichotomous
     Sampler.  Environ. Sci. Technol. 12(6):679-682, 1978.

10.  Marple, V.A., and B.Y.H. Liu.  Characteristics of Laminar
     Jet Impactors.  Environ. Sci. Technol. 8 (7):648-654, 1974.

11.  Marple, V.A., and C.M. Chien.  A Theoretical Study of Virtual
     Impactors.  University of Minnesota,  Particle Technology
     Laboratory Publication 378, 1978.  Submitted to Environ.
     Sci. Technol.

12.  Hassan, Y.A., B.C. Jones, and T.J.  Yule.   An Analytical
     Study of Virtual Impactor Aerosol Separators.  To be pub-
     lished in Trans. Am.  Nucl.  Soc., San Francisco Meeting,
     1979.

13.  Marple, V.A., N.J. Barsic,  and K.T. Whitby.  Instruments
     and Techniques for Dynamic Particle Size Measurements of
     Coal Dust.  University of Minnesota,  Particle Technology
     Laboratory Publication 215, 1974.

14.  Fuchs, N.A.  The Mechanics of Aerosols.   Pergamon Press,
     New York, 1964.

15.  Loo, B.W., and C.P.  Cork.  High-Efficiency Virtual Impactors.
     Submitted to Environ. Sci.  Technol.
                                21

-------
                             PAPER  2
             A THEORETICAL STUDY OF VIRTUAL IMPACTORS
                         VIRGIL A. MARPLE
                          CHUNG M. CHIEN
                  PARTICLE TECHNOLOGY LABORATORY
                MECHANICAL  ENGINEERING  DEPARTMENT
                      UNIVERSITY  OF MINNESOTA
ABSTRACT
     The characteristics of virtual impactors have been deter-
mined by the numerical solution of the Navier-Stokes equations
and of the equations of motion of the particles.  The effect
of the nozzle Reynolds number, the fraction of flow passing
through the collection probe, collection probe diameter, nozzle
throat length, nozzle-to-collection probe distance, and collec-
tion probe inlet design on the small and large particle collec-
tion efficiencies has been studied.  In addition, it was found
that some particles would impact on the inner surface of the
collection probe.  The results show that most parameters, with
the exception of the nozzle Reynolds number, have little effect
on the large particle collection efficiency.  However, the effect
on the small particle collection efficiency and collection probe
losses was significant for many of these parameters.

INTRODUCTION

     The virtual impactor is a device used for the inertial sepa-
ration of airborne particles.1'2  In this impactor, shown sche-
matically in Figure la, a jet of particle-laden air is directed
at a collection probe which is slightly larger in diameter than
the acceleration nozzle.  The large particles cross the air
streamlines and enter the collection probe, while the small par-
ticles follow the air streamlines into the side passage.  To
remove the large particles from the collection probe, a fraction
of the total flow passing through the nozzle of the virtual
impactor is allowed to pass through the collection probe.  This
flow will be referred to as the minor flow, while the flow through
the side passage will be referred to as the major flow.
                                22

-------
                         TOTAL FLOW
                                                    MAJOR
                                                    FLOW
       TRAJECTORY OF
       PARTICLE TOO
       SMALL TO BE
       COLLECTED

      TRAJECTORY OF
      COLLECTED
      PARTICLE
                            COLLECTION PROBE
                          MINOR
                          FLOW
                   (a) VIRTUAL IMPACTOR
        100
     u
                  REGION 1
100% -SMALL
PARTICLE
COLLECTION
EFFICIENCY
                                            REGION 3
                                      LARGE PARTICLE
                                      COLLECTION
                                      EFFICIENCY

                                      IDEAL LARGE
                                      "PARTICLE
                                      COLLECTION
                                      EFFICIENCY
                       PARTICLE DIAMETER, Dp


        REGION 1 - PARTICLES IN THE MAJOR FLOW
        REGION 2 - PARTICLES IMPACTED ON COLLECTION PROBE
        REGION 3 - PARTICLES IN THE MINOR FLOW

                (b) COLLECTION EFFICIENCY CURVES

Figure 1. Nomenclature, streamlines, particle trajectories, and efficiency
        curves for a virtual impactor.
                            23

-------
     As is the case with real impactors, the virtual impactor's
performance is characterized by a collection efficiency curve.
For the ideal virtual impactor, the separation between the large
and small particles should be perfectly sharp, as shown for the
ideal case in Figure Ib.  Note, however, that in the virtual
impactor, there will always be some of the small particles in
the large particle fraction due to the air flow through the
collection probe.

     In an actual virtual impactor, the efficiency curve is not
quite so simple, since there are not only large particles passing
through the collection probe and small particles passing through
the side passage, but also a fraction of the particles impacting
upon the inner surfaces of the collection probe.  Thus, as shown
in Figure Ib, there are actually two efficiency curves separating
the particles into the following three regions:  (1) small par-
ticles passing out the side passage,  (2) particles which are
impacted upon the collection probe  (losses), and (3) large par-
ticles passing through the collection probe.  Since losses in
the virtual impactor are highly undesirable, an impactor should
be designed such that the displacement of the two efficiency
curves shown in Figure Ib is as small as possible, with the two
efficiency curves coinciding for the desirable case of a virtual
impactor with no losses.

     It is the purpose of this paper to use numerical methods
to determine the flow fields, particle trajectories, and finally,
the efficiency and loss curves for virtual impactors operating
at different conditions of Reynolds numbers, fraction of flow
passing through the collection probe, and virtual impactor de-
sign.

THEORETICAL TECHNIQUES

     The method used to theoretically analyze the performance
of the virtual impactor is to first determine the flow field
within the impactor by solving the Navier-Stokes equations using
numerical analysis techniques, and then to solve for the particle
trajectory within this flow field by numerically integrating
the particle's equation of motion.  This method has been used
successfully in a fundamental study of real impactors to deter-
mine the influence of various parameters on the characteristic
collection efficiency curves.3  Comparisons of the  theoretical
efficiency curves with those of experimental investigationslt~8
have shown that the agreement is good if the impactor inlet con-
ditions, shapes, and Reynolds numbers are similar.  Since the
flow field and particle trajectories are similar in real and
virtual impactors, this theoretical technique should be equally
successful in determining the efficiency curves of  virtual im-
pactors.
                               24

-------
     The general method of solution of the flow field is to first
express the Navier-Stokes equations in terms of the vorticity
and the stream function.  The resulting differential equations
are then made dimensionless, with the radial, r, and axial, z,
dimensions being in units of the nozzle throat diameter, Dfl.
The Reynolds number ,

                    Re = P D° V°                              (1)
                            y

where p is the fluid density, VQ is the mean fluid velocity at
the nozzle throat, and y is the absolute viscosity of the fluid,
will be a parameter in these equations.  The dimensionless dif-
ferential equations are next expressed in a finite difference
form and solved by the method of relaxation over a grid of node
points covering the field of interest, as shown in Figure 2a.
(Note that the flow is symmetrical about the centerline.) Although
the solution is the determination of the vorticity and stream
function values at each node point, the values of the velocity
components at the node points can be calculated from the stream
function values.  For details on the derivation of the finite
difference equations, boundary conditions, and relaxation tech-
nique, the reader is referred to a previous paper by Marple et al.9

     After the flow field has been determined, it is then neces-
sary to follow particle trajectories through the virtual impac-
tor.  To accomplish this, the particle's equations of motion
in the r and z directions are made dimensionless by again express-
ing the r and z dimensions in units of D0.*  For these equations,
the Stokes number, St, defined by Fuchs1Q as the ratio of the
particle stopping distance to D0/2, will be a parameter.  The
Stokes number is thus expressed as

                          P  V0 C D 2
                    St  =  P       P                          (2)
                    St       9 M D0                           U}

where pp is the particle density, C is the Cunningham slip cor-
rection, and Dp is the particle diameter.  Since St is dimension-
less, Equation 2 indicates that /St is a measure of the dimen-
sionless particle diameter.  The dimensionless equations of
motion are next put in finite difference form and integrated
numerically through the area of interest.  This technique, which
is described in detail by Marple and Liu,1* is capable of describ-
ing the particle's trajectory once the particle's initial posi-
tion and velocity have been given.

     The integration_process is started by first assigning a
specific value of /St to a particle, and giving the particle
an initial velocity equal to the local fluid velocity at a position
                               25

-------
near the entrance.  By use of the Runge-Kutta integration method,
the movement of the particle, Az and Ar ,  during a small increment
of time, At, is determined.  This gives the position of the par-
ticle at the end of the time increment.  This process is then
repeated, and the movement of the particle through the impactor
is followed until the particle either exits through the collec-
tion probe, exits to the side of the virtual impactor, or impacts
upon the wall of the collection probe.

     The particle is considered impacted when the center of the
particle comes within one particle radius, rp, of a surface.
Since all dimensions of the virtual impactor are in units of
the nozzle diameter, D0, the particle radius must also be expressed
in units of D0.  Thus, from Equations 1 and 2,
                    JB. - J4-5 P st
                    Do   f Pp Re

A detailed description of the numerical procedure and the com-
puter program used has been given by Marple.3

RESULTS

     As described above, the flow fields, particle trajectories,
and corresponding efficiency curves of a virtual impactor will
depend on the parameters Re and Q!/QO and the physical design.
Referring to Figure 1, the design can be specified by the values
of DI/DO, LQ/DO, S/D0f and 00, and the shape of the entrance
to the collection probe.

     To initiate the parametric study, a set of base values for
the parameters were chosen and are listed in the "boxed in" por-
tion of Table 1.  The other values of the parameters in Table 1
were then varied one at a time to the values listed, while the
remaining parameters remained at the base values.  Following
is a discussion of the results for the base case, and then dis-
cussions of the effects of the various parameters.

Base Case

     The grid used for the base case, corresponding to the param-
eters in Table 1, is shown in Figure 2a.  A thin-walled tube
collection probe, which simulates a collection probe with its
wall tapered to a sharp edge at the entrance, was chosen, since
this design introduces no new variables such as wall thickness,
or radius of curvature of the probe entrance.

     The flow field streamlines for the base case are shown in
Figure 2b for streamlines corresponding to 5%, 10%, 20%, 40%,
80%, and 100% of the flow inside that streamline.  Note that
                               26

-------
the 0% streamline is at the centerline, the 10% streamline inter-
sects the collection probe (Qi/Q0 = 10%), and the 100% stream-
line corresponds to the nozzle wall.  Also note that the free
streamline emitted from the nozzle reattaches to the surface
defining the nozzle exit plane, forming a recirculation between
that surface and the free streamline.  A second recirculation
region is formed between the air flowing out the side passage
and the lower surface, causing a 5% streamline to be indicated
in this region.

     In Figure 3a, the particle trajectories for five particles
with different values of /St, all starting at the 50% streamline,
are shown.  These five particle trajectories include the three
cases where particles (1) pass through the collection probe,
(2) are impacted on the collection probe inner surface, and  (3)
pass through the side passage.  Also included are the two critical
trajectories^ between these three cases.  For example, if the
value of /ST  of a particle is greater  than 0.881,  the particle
will pass through the collection probe; if it is less than 0.677,
the particle will pass through the side exit; and if it is be-
tween these two critical values, the particle will  impact on
the collection probe inner surface.

       TABLE 1.  VALUES OF DESIGN PARAMETERS USED IN STUDY	
  Re
Qi/Q.
Lo/D,
S/D,
e,
Collection
 probe3
1
10
100

(B) =| |
(C) — ' !


1,
5,
15,

500

000
000
000



0.
0.
0.
0.


05
10
15
25


1.
1.
1.



16
33
49


	 1 1
0.013 0.25 30° (D) ^ j
2.5 1 45° (A)~~||
2




b



    Collection probe A - thin wall
    Collection probe B - infinite wall thickness
    Collection probe C - finite wall thickness
    Collection probe D - finite wall thickness with  taper
    (Collection probe designs are shown  in Figure  18.)


    Base values from which parameters are varied.
                                27

-------
00
                                                                          5%
                                                                         10%
                                                                         20%
                                                                         40%
                                                                         80%
                                                                        100%
                                                                            RECIRCULATION
                                                                            REGION-^
                                                                    •    .    i. i
                                                                     RECIRCULATION
                                                                     REGION
                                                                                                    NOZZLE
                                                                                                    EXIT PLANE
                              (a) GRID
                                                            (b) STREAMLINES FOR BASE CASE
                                   Figure 2. Grid and flow field for virtual impactor at base case conditions.

-------
to
VD
                            PARTICLES STARTING
                            AT 50% STREAMLINE  —J
                           J	.,
                          y/lt
                          0.575
                          0.677
                          0.779
                          0.881
                          0.983
 PARTICLE
 TERMINATION
MAJOR FLOW	
CRITICAL	
IMPACT ON PROBE
CRITICAL	
MINOR FLOW	
                                      PARTICLES STARTING
                                      STREAMLINE
                   (a)   FIVE PARTICLES OF DIFFERENT SIZES
                       STARTING AT THE SAME POINT
                                (b)  CRITICAL TRAJECTORIES FOR
                                    PARTICLES OF SIZE V^St"= 0.5
                                           Figure 3. Particle trajectories at base conditions.

-------
     Another method by which the critical values of /St can
be determined is to keep /St constant while varying the inlet
starting position of the particle, as shown in Figure 3b.  This
shows that particles with /St = 0.5 starting between the 24%
streamline and the centerline will pass through the collection
probe, those starting between the 24% and 75% streamlines will
impact on the collection probe, and those starting at streamlines
greater than 75% will pass out the side exit.

     By using data such as represented in Figure 3a for particles
starting at several positions, or as in Figure 3b for particles
with different values of /St, the "large particle collection
efficiency" and the "small particle collection efficiency" curves
shown in Figure 4 can be determined.  In either case, the col-
lection efficiencies are the percent of particles issuing from
the nozzle which pass through the collection probe or side pas-
sage, respectively.  The value of /St as a function of these
efficiencies is presented as the base case in the two tables
of the Appendix.  Also note that this information for all cases
listed in Table 1 is presented in the Appendix.

     For the purpose of determining the percent of the particles
being impacted on the inner surface of the collection probe,
referred to as "collection probe loss" in this paper, it is best
to construct the curve "100% - small particle collection effici-
ency".  This curve, along with the large particle collection
efficiency curve, represents the two efficiency curves in Figure Ib.
As seated before, the difference in the efficiencies at any value
of /St represents the collection probe loss, and thus the loss
curve can be constructed.

     It should be noted in Figure 4 that the collection charac-
teristics of a virtual impactor can be specified by the large
particle collection efficiency curve and any one of the other
three curves.  However, since the collection probe losses are
of considerable importance, this curve will be used in this paper.
Also note that the quantity of collection probe losses is quite
large, being greater than has been reported in experimental in-
vestigations.11'12  However, investigations of the computer out-
puts indicated that nearly all losses occurred at the tip of
the collection probe by particles that were traveling vertically
upward directly adjacent to the probe inner surface.  As shown
later, by proper contouring of the probe entrance, it is possible
to reduce these losses.  Therefore, the absolute values of the
losses in this paper may be high, but the relative effects of
the various parameters on these losses are of interest.

     Although the contour of the collection probe entrance af-
fects the probe losses, it has little effect on the large par-
ticle collection efficiency curve.  Thus, this curve should be
considered as the most significant characteristic curve for
virtual impactors, and it is the curve by which virtual impactors
will be characterized in this paper.
                               30

-------
      100
      80
CO
CO
O

O
Z
<

O

ill
O
   O
   Ul
   O
   O
      60
      40
       20
                             T
                    100% -SMALL PARTICLE
                    COLLECTION EFFICIENCY
                        CD-
            SMALL PARTICLE
            COLLECTION EFFICIENCY
            Re = 5000
         0-,/Qo = 0.10
               1.33
               2.5
          s/D0 = 1
            00 = 45°
0
0.1
                                                 LARGE PARTICLE
                                                 COLLECTION
                                                 EFFICIENCY
FRACTION IMPACTED
ON COLLECTION
PROBE (LOSS)
                                          I   I   I  I
                                      0.5
                                                1.0
                2.0
           Figure 4. Collection efficiency and loss curves for base conditions.

     It  is  of  interest to compare  the large particle collection
efficiency  curve determined theoretically to experimental  curves
by other  investigators in Figure 5.   The values of the  parameters
listed in Figure 5 for each curve  indicate that the virtual im-
pactors  are similar.   The comparison  shows that the theory agrees
well with the  experimental curves  of  Loo11 and McFarland et al.12
The theoretical curve is nearly identical to Loo's experimental
curve, with the experimental curve of_ McFarland et al.  having
approximately  20% lower values  of  /St.

Influence of Reynolds Number

     To  determine the influence of the Reynolds number,  cases
were run  for the different values  of  Re listed in Table  1,  while
the other parameters  were held  constant at base values.   The
flow fields are shown in Figure 6  for Re = 1, 10, 100,  500, 1,000,
and 15,000,  and in Figure 2b for Re = 5,000.   In Figure  6,  only
the portions of the flow fields in the vicinity of the  collection
probe are shown, since the flow fields in other portions of the
impactors are  very similar to those in Figure 2b.  It should
be noted  that  the flow may not  be  laminar for Re = 15,000,  but
is presented as a limiting case.
                                31

-------
        100
         80
      n-  60
     o
     LLJ
     o
     LL
     LL
     UJ
         20
                      THEORY
PRESENT WORK

   EXPERIMENTAL
   LOQ11
   McFARLANDl2
          0.1
               0.5
1.0
                                                             2.0
                                   \/~St~
Figure 5. Comparison of theoretical and experimental large particle collection
       efficiency curves at the following conditions:
                                Re   QJ/QO  s/D0   DJ/D
         Present theory           5000    0.1   1.0     1.33
         Looll                 6000    0.1   0.8     1.38
         McFarland12            4500    0.1   0.9     1.31
          2.5
          0.8
                                            e0
                                           450
                                           450
     Since  the large particle  collection efficiency curves are
of primary  interest, the flow  fields within  the  collection probe
are of most importance.  It  is in this region where we observe
the unexpected result that the penetration of the 10% and 20%
streamlines into the collection probe is greater for the cases
of Re =  100 and 500 instead  of for the higher values of Re, where
the inertial effects of the  flow should be larger.   The reason
for this can be seen by inspecting the velocity  profiles at the
nozzle exit plane shown in Figure 7.  At high values of Re  (Re =
5,000 and 15,000), the velocity profile is relatively uniform
across much of the nozzle, making it difficult  for  any portion
of the flow to penetrate into  the air in the collection probe.
For the  cases of Re = 500 and  100, the velocity  profile is more
parabolic,  and the relatively  high velocity  near the centerline
makes it possible for the jet  to penetrate farther  into the col-
lection  probe.  However, if  the value of Re  is  small  (Re = 10),
there is insufficient inertia  in the jet to  penetrate into the
                                 32

-------
                                       :si
                                        sli
                          ••*
                             .-••*
                 Re = 1
U)
                  Re = 500
                                     •/.'S
                                      » it*
                                       I*
                                       °   i»
lit
                                     iVw^
                                      VJ!
                                           ii
                                                                       ..•••::"j»gs?
                                                                         ,' ** «   -V
                    Re= 10
                                                                                  •   l»


* A i * ***ii>ii%
^H
-.•^


Re = 1000
4 •**!
* "•»
» •**
4 •**
y ::s
• • •*«
'/i--
ufe
U?

; f
* »
0
.
Re = 100
                                                                                                        Re = 15,000
                                                                                                                         a  ,-aj
                                                                                                                             /
                                                                                                                                :L
                                                                                   *i  /I-*-
                                                                                    -   ,v|
                                                                                       /. I''
                                    Figure 6.  Theoretical streamlines at the specified values of Re
                                                    = o. 1, DJ/DQ = 1-33, LO/DO = 2.5, S/DO = 1, and e0 = 45°).

-------
                      DISTANCE FROM AXIS, r

          0.5     0.4     0.3      0.2     0.1
Figure 7. Influence of the Reynolds number on the axial velocity profile at
         the nozzle exit.
                                 34

-------
viscous air in the collection probe.  Thus, Re in the range of
100 to 500 is the correct combination of nozzle velocity profile
and inertia to obtain maximum penetration of the 10% and 20%
streamline into the collection probe.

     The large particle collection efficiency curves and loss
curves are shown in Figure 8 with Re as a parameter.  The in-
fluence of the flow penetration into the collection probe can
be seen in the position of the large particle collection effi-
ciency curves in Figure 8a.  For the cases where the flow pene-
tration into the collection probe is largest (Re = 100 and 500),
the particle Stokes numbers must be larger in order for the par-
ticles to penetrate into the minor flow, since the Stokes number
is defined as the ratio of the particle stopping distance to the
radius of the nozzle.  Where the flow penetration into the collec-
tion probe is small, the required distance that the particle must
travel, and thus the value of the Stokes number, will be smaller.

     It is of interest to note in Figure 8a that the efficiency
curves are nearly identical for the cases of Re = 1 and 10, and
for Re = 5,000 and 15,000, indicating that lower or higher Rey-
nolds numbers than those listed should have little effect on these
curves.  It is also interesting to note that the slopes of the
penetration curves are greater for the larger values of Re, in-
dicating better cut-off characteristics.  However, this effect
is small, which is different from real impactors, where the cut-
off characteristics are much poorer for low values of Re than
for large values.1*

     Concerning the influence of Re on the losses, Figure 8b
shows that the influence is large.  In general, the losses in-
crease from a minimum of about 10% at low values of Re to about
60% at high valjjes of Re, with the maximum losses occurring at
the value of /St corresponding to 50% efficiency.

Influence of Qi/Q0
     The flow fields corresponding to Qj/Qo values of  0.05,  0.15,
and 0.25 are shown in Figure 9, and should be compared  to  the
base case of Qi/Q0 = 0.10 in Figure 2b.  As can be seen from
these figures, more streamlines pass through the collection  probe
for large values of Ch/Qo and the small amount of flow  in  the
side passage leaves more room for recirculation in this area.
Tne flow field for Q^/Q0 = 0.05 shows reattachment to  the  lower
surface of the side passage, much like the flow at Re  = 100  in
Figure 6.  Whether or not the flow field in this region is cor-
rect is uncertain.  However, since the flow in the region  has
no effect on the flow field in the important area within the
collection probe, a more detailed investigation of the  flow  in
this region was not made.

     The corresponding large particle collection efficiency  curves
and loss curves are shown in Figure 10.  The large particle  col-
lection efficiency curves indicate that a "sharper" cut between


                               35

-------
oo
          I
           Po

           S  £
              o
              o
              I-
              I-

           a  $

           I  l
      o
      00
      m
         II  Q.
        \o
        O=s
           5
Co



r-
               O
               vt
               v>
                      p
                      is)
                                   COLLECTION PROBE LOSS, %




                                  8         §         g        §
                      fO

                      o
                                                                 8

-------
w
          p


           o
          o
           ii

           p
           N9
           a\
                                p

                                en
""""°"°^aSSaSiSSiHiiJHjS 8_8_8
                                                                     pew **"«* •»•*««••»*• •• •« • * •* »•

                                                                        •*"*aai?J8S«83 j i S si H 1 1 88
 O
o

 ii

 p

 b
 (D
                                                                             or   sc     oc
                                   Figure 9.  Theoretical streamlines at the specified values of Q 1/Q.Q (Re = 5000,

                                                    = 1.33, LQ/DO = 2.5, S/D0 = 1, and 60 = 45o).

-------
            I
CD
^   ff
-  S e*   —
»a.8.   g
        r~
          35 «•
  §
              '
03?
—» O
            Q)
    8
  *>§'
  -* --3
  b|

  ^ I

  gf

  r-S

  %i
  CJ
               p
               ro
a


o


-o
yj
O
m
m
                 O  <$
                       p

                       VI
 COLLECTION PROBE LOSS, %


       3       B
—	1	\	
                                                 8
                                                T~
                                                                   o
                                                                   o
                                                    p p p p


                                                    O W O 

          Pi

-------
large particles collected and those which are not is obtained
for smaller values of Qi/Qo-  Also, the cut-off size increases
as Qi/Qo decreases.  This is expected, since particles must pass
through more air to enter the minor flow stream when Qi/Q0 is
small.

     The loss curves show more losses associated with the lower
Qi/Qo values.  This would be due to the larger percentage of
the flow being exposed to the inlet of the collection probe where
the losses generally occur, and should be decreased with proper
inlet design.

Effect of Pi/Dp

     Besides DJ/DQ being equal to the base value of 1.33  (Fig-
ure 2b), D!/DO was also set at 1.16 and 1.49 (Figure 11).  Al-
though, as shown in Figure 12, this parameter had only a small
effect on the large particle collection efficiency and loss
curves, there are substantial differences in the flow fields
for these three cases.  For example, the flow field attaches
close to the nozzle exit when D!/DO = 1.49 but does not attach
when D!/DO = 1.16.  Experiments (personal communication from
B.W. Loo, Lawrence Berkeley Laboratories) have shown that for
values of D!/DO on the order of 1.49, the reattaching flow does
cause particles to impact on the nozzle exit plane surface,
increasing the losses in the virtual impactor.   Therefore, it
is recommended that the value of Di/D0 be kept less than 1.49
and preferably near 1.33.

Effect of L0/D0
     To investigate the effect of L0/D0f the  results of  a  case
where L0/D0 is small  (L0/Do = 0.013)  is compared  to the  base
case.  Although the streamlines  issuing from  the  nozzle  are
not parallel to the nozzle axis  when  L0/D0 =  0.013  (Figure 13)
as they were when L0/D0 =2.5 (Figure 2b) , the effects on  the
large particle collection efficiency  and the  loss curves are
negligible, as shown  in Figure 14.  Similar insensitivity  to
this parameter was found for real impactors.

Influence of
     The influence of S/Do was determined by using values of
S/DO = 0.25, 1  (base), and 2.  The flow fields  shown  in  Figures
15 and 2b appear to be quite different.  However, in  the region
in the collection probe where the 10% streamline attaches to
the probe wall, the flow fields are similar.  Thus, as expected,
the resulting large particle collection efficiency curves shown
in Figure 16 are nearly identical.  Again,  this is different
from the effect found for real impactors ** where small values
of S/D0 have a large effect on collection efficiency.
                               39

-------
              i   i  4
                          1.16
                                              A «*» I
                                              A ««• L
                                              A ««V j»
                                               •«w|
 JA «*W
 JA ••«•
 /* •*»
|y.*"
^f*
:
-------
                         COLLECTION PROBE LOSS,
So
;n   e
§.§
    Q.

    8
§
    01
a

o
   o
   00
   m
        V)
              p

              U1
              ro
              b
                        g
                                   §
                                                8
                                                 a
                                                 o
o
o
                                                           m
                                                           •o
                                                   o
                                                   r-
                                                   rn

                                                   o
                                                   O
                                                   r-
                                                   r-
                                                   m
                                                   o


                                                   O
                                                   z

                                                   m
                                                           m

                                                           O
EFFICIENCY, E (%)




   S       §
                                                                                          *» w -»
                                                                                          (O W O)
                                                                                          t> O D
                                                                                                     a
                                                                                                    o

-------
                                              15 10  .5   1
/5.   Theoretical streamlines at LQ/DQ= 0.013 (Re = 5000, QJ/QQ = 0.1,
           = 1.33, S/D0 = 1, and 60 = 45°).
                          42

-------
                100
            55


            lif
            o


            LU

            O

            EZ
            LL
            LU
                 20 -
           V)

           8
           LU
           03
           O
           cc
           a.
           O
           o
                                     0.5            1.0


                                          V^st"


                    (a) LARGE PARTICLE COLLECTION EFFICIENCY


                100 i	1	1	1	1	1—I—n	
                 80
60
                 40
                 20
                                                 2.0
  0.2                 0.5            1.0


                         \/St~


   (b) COLLECTION PROBE LOSS
                                                                  2.0
Figure 14.   Large particle collection efficiency and collection probe loss curves

            at the specified values of LQ/DQ (fie = 5000, Qj/Qn = 0.1, DJ/DQ = 1.33,

            S/D0= 1, and Q0
                                       43

-------
»    5   s  s  ; ;.;*•:>.
           = 0.25
       i  i  •
           = 2
Figure 15.   Theoretical streamlines at the specified values of S/DQ (Re = 5000,
                   = 1.33, L/D  = 2.5, and Q= 45O).
                                                    = 0. 1,
             44

-------
                   100
                    80
                    60
                u

                >
                u
                    40
                 LL
                 U.
                 HI
                    20
                                S/DQ
                                0.25 O
                                1    O
                                2    A
                       0.2
           0.5
1.0
                                                                     2.0
                        (a) LARGE PARTICLE COLLECTION EFFICIENCY
                    100
                    80
                 CO
                 8
                 ui
                 §  60
                 cc
                 a.
                 O
                 O
                    40
                    20
                                                 i  I  *
                                                        I
S/Dr
                       0.2
0.5
                         1.0
              2.0
                        (b) COLLECTION PROBE LOSS

Figure  16.  Large particle collection efficiency and collection probe loss curves at the
           specified values of S/Drj (Re = 5000, G//Q0 = °-1> Dj/D0 = 1-33,  LQ/DQ = 2.5,
           and do = 450).
                                         45

-------
     However, the probe loss curves shown in Figure 16 are in-
fluenced by S/Do, with larger losses being found with small S/D0
values.  It may be expected that additional losses will be ex-
perienced on the nozzle exit plane surface and on the backside
of the collection probe for small S/D0 values due to turbulence
in the restricted area between the collection probe and nozzle
exit plane.

Influence of 00
     The effects of the entrance angle on the large particle
collection efficiency and probe loss curves are shown in Fig-
ure 17.  Since the streamlines are very similar to the base case
shown in Figure 2bf the streamlines for 60 = 30° are not shown.

     From Figure 17, it can be seen that the large particle col-
lection efficiency curves are similar in shape for both angles,
but the curve for 00 = 45° is shifted to smaller particle sizes.
This is due to the particles being thrown closer to the center-
line for the larger 90 values, making the collection of particles
in the probe slightly easier.  The losses shown in Figure 17
indicate less loss for 00 = 45° than for 60 = 30°.  Thus, it
appears that 00 should be at least 45°.

Influence of the Collection Probe Inlet Design

     Four receiving tube configurations were tested as shown
in Figures 2b and 18.  The base design was a thin wall shown
as configuration A.  In configuration B, the wall was infinite
in width, and in configuration C, the wall had a finite thickness,
In configuration D, the wall thickness was also finite, but the
inner surface was tapered in an attempt to reduce losses.

     The flow fields for these configurations are shown in Fig-
ure 18, and the resulting large particle collection efficiency
and probe loss curves are shown in Figure 19.  Since configura-
tion B is essentially a real impactor impaction plate with a
hole in its center, particles are collected on the plate, and
thus losses are meaningless for this case and are not shown.

     It is interesting to note that the configuration of the
entrance to the collection probe had essentially no effect on
the large particle collection efficiency curve.  This would be
expected, since this curve defines the separation of particles
which impact upon the probe wall and those which pass .through
with the minor flow, and since the region of importance for this
curve is inside the collection probe rather than at its entrance.

     The losses, however, are influenced by the collection probe
configuration.  For configurations where there is a sharp edge
at the upper entrance, such as configurations A and C, the probe
losses are quite large and the loss curves are similar.
                               46

-------
               100
                80
               GO
           u
           —
           o

           4-   40
                20
                         1	r
                          30°

                          45°
                 0.2
0.5
                                                 1.0
2.0
                    
-------
I	1	1	1	1 . I 1 . . 1 . 1 H fi i ±1 F//5
    COLLECTION PROBE B
     1   '  i  » I
      COLLECTION PROBE C
                                     
-------
  I
 5;
O -Q JB

 :i 3 §.
 -»s-9
  
  .-^
  &
  to
                      NJ
                      o
                                        o
                                        o
                                      CO
                                      o
o
o
       m
§   <
?   »i
             p

             Ol
       v>
       V)
             N)

             b
                             D

                            -L
                                      >

                                     -L
                                  o

                                 •  L.
                                              m
                                              n
                                              O
                                              00
                                              m
o
o
                                                              p
                                                              ro
    33
    O
    m


    Z
    73
    H

    a
    t-
    m

    O
                                                        m
                                  00
                                                                     •L - L   JL  -L
a
o
r-
i-
m
n

-------
     The losses that were found in these cases are from particles
which are traveling vertically upward along the collection probe
wall toward the major flow exit.  The boundary layer in this
region is very thin, and particles passing within one particle
radius of this wall are collected as a loss.  If there were some
mechanism, such as aerodynamic forces, which would keep the par-
ticle from touching the wall, it would not be collected as a
lost particle.

     In addition, losses should be reduced by replacing the sharp
corner in configuration C with a tapered entrance  (configuration
D) so that the particles could not be collected as easily at
the upper corner of the probe.  As shown in Figure 19b, the
losses were reduced.  By replacing the taper with a radius, the
losses should be reduced even farther.

CONCLUSIONS

     An examination of the large particle collection efficiency
curves reveals that they all have essentially the same shape
and are not greatly influenced by any of the parameters.  The
only parameter which appears to influence the shape is Ql/Q0,
because the collection efficiency curves are_ajsymptotic to the
different values of Qi/Qo at low values of /St.

     The reason none of the parameters has a large effect on
the large particle collection efficiency curve is that this ef-
ficiency is governed by the flow field within the collection
probe.  The losses, however, are governed by the flow conditions
at the tip of the collection probe inlet, and thus are influenced
by many of the parameters.  This is especially true for the case
of the collection probe inlet design, where losses were reduced
by adding a taper to the probe inlet.

ACKNOWLEDGEMENT

     This work was supported under Bureau of Mines Contract H0177026
through the Twin Cities Mining Research Center.  The financial
support of the Bureau is gratefully acknowledged.  This report
is Particle Technology Laboratory Publication No.  378.

REFERENCES

  1.  Loo, B.W., J.M. Jaklevic, and F.S. Goulding.  Dichotomous
     Virtual  Impactors for Large-Scale Monitoring of Airborne
     Particulate Matter.  In:  Fine Particles:  Aerosol Genera-
     tion, Measurement, Sampling, and Analysis, B.Y.H. Liu, ed.
     Academic Press, New York, 1976.  pp. 311-350.

  2.  Dzubay,  T.G., and R.K. Stevens.  Ambient Air Analysis with
     Dichotomous Sampler and X-Ray Fluorescence Spectrometer.
     Environ. Sci. Technol. 9:663-8,  1975.
                               50

-------
 3.   Marple,  V.A.   A Fundamental Study of Inertial Impactors.
     Ph.D.  Thesis,  University of Minnesota,  Mechanical Engineer-
     ing Department, Particle Technology Laboratory Publication
     144, 1970.

 4.   Marple,  V.A.,  and B.Y.H. Liu.   Characteristics of Laminar
     Jet Impactors.  Environ. Sci.  Technol.  8:648-654, 1974.

 5.   Jaenicke,  R.,  and I.H.  Blifford.   The Influence of Aerosol
     Characteristics on the  Calibration of Impactors.  J. Aerosol
     Sci. 5:457-464, 1974.

 6.   Willeke, K.,  and J.J. McFeters.  The Influence of Flow Entry
     and Collecting Surface  on the  Impaction Efficiency of Inertial
     Impactors.   J. Colloid  Interface  Sci.  53:121-7, 1975.

 7.   Schott,  J.H.   Jet-Cone  Impactors  as Aerosol Particle Sepa-
     rators.   M.S.  Thesis, University  of Minnesota, 1973.

 8.   Willeke, K.   Performance of the Slotted Impactor.  Am. Ind.
     Hyg. Assoc.  J. 36:683-691, 1975.

 9.   Marple,  V.A.,  B.Y.H.  Liu, and  K.T. Whitby.  On the Flow
     Fields of Inertial Impactors.   J. Fluids Eng.  96:394-400,
     1974.

10.   Fuchs, N.A.   The Mechanics of  Aerosols, Pergamon Press,
     New York,  1964.  p.  154.

11.   Loo, B.W.,  and C.C.  Cork.  High Efficiency Virtual Impactor
     for Collecting Airborne Particulate Matter.  Lawrence Berkeley
     Laboratory Report LBL-8204, 1978.

12.   McFarland,  A.R., C.A. Ortiz, and  R.W. Bertch, Jr.  Particle
     Collection Characteristics of  a Single-stage Dichotomous
     Sampler.  Environ.  Sci. Technol. 12:679-682, 1978.

 APPENDIX

      The values of /St for  the large  particle and small particle
 collection efficiency curves are tabulated in Tables A-l and
 A-2, respectively.  The  cases are  the same as those listed in
 Table 1.  The base case  is  presented  first and subsequent cases
 are labeled by the value of the changed variable.  For example,
 for the case Re =  1, all variables except Re are at the base
 values.

      The large particle  collection efficiency curves are pre-
 sented in the appropriate figures.  The small particle collection
 efficiency curves  are not presented,  but were used to determine
 the collection probe loss curves as described in Figure 4.  The
 collection probe loss curves are then presented in this paper.
                                51

-------
   TABLE A-l.   VALUES OF /St FOR THE LARGE PARTICLE COLLECTION
                        EFFICIENCY CURVES

Case 16%
Base
Re = 1
10
100
500
1,000
15,000
Qj/Qo = 0.05 0.57
.15
.25
Di/Do = 1.16
1.49 .37
Lo/Do = 0.013
S/Do =0.25
2
Go = 30°
Collection Probes a
(B)
(C)
(D)
Large particle
23% 35% 50%
0.48 0.59
.42 .53
.40 .51
.54 .67
.56 .70
.51 .64
.48 .59
.73
.34 .49
.29
.57
.51 .62
.48 .58
.47 .58
.49 .60
.65

.57
.59
.59
0.67
.62
.60
.76
.80
.73
.67
.79
.59
.45

.71
.67
.65
.69





collection efficiency
60% 70% 90% 98%
0.71
.67
.66
.82
.85
.77
.71
0.85
.64
.57
.69
.80

.73

.78

.69
.71
.71
0.84
.88
.86
1.02
1.03
.94
.83
.93
.78
.69
.80
.89
.85
.87
.87
.96

.80
.83
.84
1.01
1.22

1.34
1.41
1.23
1.00
1.11
.96
.86

1.13
1.06
.98
. 1.07






a  Collection probe A - thin wall
   Collection probe B - infinite wall thickness
   Collection probe C - finite wall thickness
   Collection probe D - finite wall thickness with taper
   (Collection probe designs are shown in Figure 18.)
                              52

-------
 TABLE A-2.  VALUES OF /St FOR THE SMALL PARTICLE COLLECTION


Small particle
Case 84% 77% 65%
Base
Re = 1
10
100
500
1,000
15,000
QX/QO = 0.05 0.23
.15
.25
DX/DQ = 1.16
1.49
LQ/DO = 0.013
S/DQ = 0.25
2
e0 = 30°
Collection Probes3
(B)
(C)
(D)
0.23 0.39
.35 .46
.35 .47
.41 .57
.34 .54
.28 .45
.24 .39
.46
.32
.08
.40
.23 .43
.23 .38
.10 .31
.29 .44
.43

	
.34
.45


collection
50% 40%
0.47
.55
.56
.68
.66
.55
.47
.53
.43
.32

.52
.46
.40
.53





0.51
.60
.61
.75
.72
.59
.51

.48
.39
.51




.55

	
.47
.57

efficiency
30% 10%
0.58
.79
.79
.96
.92
.71
.58
0.58 .60
.56
.45 .53
.59
.61 .67
.53 .56
.46 .49
.60 .64
.62

	
.54
.65

2%
0.64
1.00

1.23
1.13

.64
.66
.63
.60

.74
.63
.55
.69






a  Collection  probe  A -  thin  wall
   Collection  probe  B -  infinite wall thickness
   Collection  probe  C -  finite wall thickness
   Collection  probe  D -  finite wall thickness with  taper
   (Collection probe designs  are shown in Figure 18.)

                              53

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                              PAPER  3
                  A HEAVY GRAIN-LOADING IMPACTOR
                         DALE A. LUNDGREN
                         ERNEST R. CERINI
                       UNIVERSITY  OF  FLORIDA
         DEPARTMENT OF ENVIRONMENTAL ENGINEERING SCIENCES

                                AND

                         MICHAEL L.  SMITH
                      ANDERSEN  SAMPLERS,  INC.
ABSTRACT
     This paper discusses a heavy grain-loading impactor  (Ander-
sen Model HCSS) which was designed for use in high grain loading
applications, where standard impactors cannot be used because
of collection surface overloading.  The HCSS consists of two
impaction chambers followed by a cyclone and glass fiber thimble.
Construction of stainless steel allows its use in the high tem-
perature, corrosive gas atmosphere encountered in industrial
stack gas sampling.

     Descriptive information on the HCSS is presented together
with particle size collection characteristics.  Data on the mass
loading characteristics for a mineral dust aerosol are presented.
Application areas are cited.

INTRODUCTION

     The Andersen Model HCSS is a special application in-stack
size-fractionating sampler developed specifically for particle
size distribution measurement in high aerosol mass concentration
gas streams  (2 to 200 grams/m3 or 1 to 100 grains/ft3).  Other
commercially available in-stack impactors typically have mass
deposit limitations on the order of 1 to 10 milligrams per stage,
for mineral type aerosols, to avoid particle reentrainment prob-
lems.  Therefore, these conventional impactors, when operating
at 14 jlpm (0.5 cfm) flow rates for 1 to 100 minute sampling times,
are best suited to sampling in aerosol concentrations ranging
                               54

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from 0.002 to 2 grams/m3 (0.001 to 1 grain/ft3), giving total
particulate matter collections of 3.5 to 35 mg.  In this new
sampler the particle fractionating stage surfaces are not coated
with grease or filter media, making the recovery of collected
material easier and chemical analysis simpler because analysis
coating reactions and analysis interferences are eliminated.
Because of stainless steel construction, sampling at high tempera-
tures is possible (a unit has been successfully field tested
at 1520°F) without the particle reentrainment problem often en-
countered when conventional impactors operate at high tempera-
tures without collection surface coatings.  This unit will fit
through a 3-inch or larger sampling port and will operate in
both the vertical and horizontal positions.  The long length
of the HCSS makes it less convenient to use in small diameter
stacks and the difficulty of accurate recovery of small mass
quantities makes it undesirable for use when sampling gas streams
with aerosol concentrations less than 0.2 grams/m3  (0.1 grain/ft3)

     Sampling of. liquid aerosols is also possible if the final
filter does not become overloaded.  The glass fiber thimble pro-
vides a very large collection surface area; therefore overloading
is unlikely with most aerosols.  When sampling in very high tem-
perature environments the glass fiber thimble is replaced by
an alundum thimble.  Because only three size fractionating stages
are used, with a last stage classification at 1.5 jam  (or optional
2.5 ym), the HCSS is not superior to, nor does it replace, con-
ventional impactors.  As stated, the HCSS is a special applica-
tion size fractionating sampler, capable of giving good particle
size distribution data in high aerosol mass concentration gas
streams  (where conventional impactors will overload and produce
incorrect particle size distribution data).

SAMPLER DESCRIPTION

     The Andersen HCSS consists of two impaction stages followed
by a cyclone stage and a glass fiber thimble filter.  This unit
is shown schematically in Figure 1.

     In use, an appropriate nozzle size is selected to enable
isokinet.ic sampling within the approximate flow rate range from
8 to 20 S,pm  (0.3 to 0.7 cfm) .  The first impactor stage has a
nominal cutpoint of 11 ym aerodynamic diameter at a 14 Jlpm  (0.5
cfm) flow rate.  The aerosol passing Stage 1 flows out through
a set of three outlet tubes (only one of which is shown in Fig-
ure 1) and into the second stage impaction nozzle.  Stage 2 is
similar in design to Stage 1 but has a nominal cutpoint of 6 ym
at the design flow rate.  Aerosol exiting Stage 2, through a
set of three equally spaced outlet tubes, next passes through
a small cyclone of the Southern Research Institute design.l A
standard 1.5 ym cutpoint cyclone is used, with a 2.5 ym cyclone
available as an option.  A high-efficiency glass fiber thimble
filter removes all remaining particle matter.
                               55

-------
                            FLOW
            ACCELERATION
                JET
         r 0
         - 5
         L10 cm
         SCALE
                 VENT
                 TUBE
                                   ISOKINETIC PROBE
                                    FIRST IMPACTION STAGE
                                    SECOND IMPACTION STAGE
                                     CYCuONE STAGE
                                     GLASS FIBER
                                     THIMBLE FILTER
Figure  1. Schematic of the Andersen Model HCSS High Grain-Loading
         Impactor (from McFarland3).
                             56

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     Both  impaction  stages  are scaled versions of the Andersen
preseparators shown  in  detail in Figure 2.  The model HCSS  first
stage has  the same internal dimensions and collection character-
istics as  the previously  tested preseparator.2  A particle  size-
collection efficiency curve for a 14.2 &pm (0.5 cfm) flow rate,
from McFarland, Ortiz and Bertch,2 is reproduced as Figure  3.
Extensive  tests were run  on this first stage separator using
a monodisperse liquid oleic acid aerosol and a polydisperse dry
fly ash aerosol.  Data  on the effect of flow rate upon outpoint
and mass loading  characteristics are shown in Figures 4 and 5
respectively  (from McFarland, Ortiz and Bertch2).

     Stage 2  is similar to  Stage 1 except for the jet dimensions.
This modification changes the cutpoint as shown in unpublished
data of McFarland3 who  determined the cutpoint of both stages
and both optional cyclones, as shown in Figure 6.  Loading  charac-
teristics of  Stage 2 and  the Southern Research Institute design
cyclone were  not  previously reported; therefore the following
performance tests were  run.

                        FLOW
                              ISOKINETIC PROBE
           ACCELERATION
             NOZZLE
           VENT
           TUBE
        Figure 2. Preseparator design details (from McFarland, Ortiz, and Bertch?).
                                57

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     100
   §  80
   i
      60
   UJ
   o
  I  40
  8 20
             O  MONODISPERSE OIL
                DROPLETS

             D  FLY ASH
                                 I
I
I
                  5             10             20       30

                 AERODYNAMIC PARTICLE DIAMETER, Dp, /an
I
              40  50
Figure 3. Preseparator particle size versus collection efficiency (from McFarland,
         Ortiz, and Bertch2).
                                 58

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              20
              15
           £
           a.
            Q.
           a
           N
           co
           t-
           o
           a.
           I-
           u
              10
                            I
I
                            10           20

                              FLOW RATE, q, Sjmm
       30
40
50
       Figure 4. Effect of flow rate upon preseparator outpoint (from McFarland, Ortiz,
              and Bertch?).

PERFORMANCE TESTS

     The loading characteristics of the HCSS second stage  (6 ym
cut-size impactor)  and third stage (1.5 ym cut-size cyclone)
were evaluated using  dry  mineral dusts:  AC Fine Test Dust  and
AC Coarse Test Dust (sometimes  referred to as Arizona Road  Dust).
These are standard  polydisperse mineral dusts of fairly well-
known size distribution.   Both  dusts were dispersed into  dry
air with a Wright Dust Feed  Mechanism. "*  Size distribution  and
concentration of the  generated  aerosol were determined by means
of a standard multi-stage impactor using grease coated stainless
steel collection surfaces conditioned at 200°F for one hour.
Sampling time and flow rate  were selected to produce near optimum
stage collection deposits.

     After the test aerosol  concentration and size distribution
were determined, the  aerosol was sampled through the first  two
(impactor) stages of  a clean HCSS and the penetrating aerosol
concentration and size distribution were again determined using
a standard multi-stage impactor.  This initial two-minute aerosol
penetration test was  run  on  the clean HCSS sampler operating
                                59

-------
               100
             ~ 80
             
-------
            100
         „  80
         c
O

01
O
         ai
         Z
         O
         o
         LU
         o
         O
             60
            40
             201
                                    \  I  I  I  I I  I
              0.7   1             3     5   7   10

                    AERODYNAMIC PARTICLE DIAMETEiR, Dp,
                                             30
       Figure 6. Particle size versus collection efficiency data for all stages of the
              Andersen Model HCSS sampler (from McFarland3).

on log normal paper,  are shown for both  the clean HCSS (noted
as initial  tests)  and the dust-loaded HCSS  (noted as final tests)
in Figure 7  for  the AC Fine Test Dust and  in  Figure 8 for the
AC Coarse Test Dust.   Actual dust quantities  collected by each
stage of the Model HCSS are also noted.  Percent  of dust pene-
trating the  second and third stage, based on  the  initial two-
minute test, the final two-minute test and  the  overall average
for the 60-  to 100-minute loading test did  not  significantly
change for  either  stage.

     Size classified mass fractions collected during the standard
multi-stage  impactor test using AC Fine  Test  Dust were used to
determine the particle size/collection efficiency of both the
second (impactor)  and third  (cyclone) stages  of the HCSS.  Mass
concentration, before and after each respective stage, was ratioed
for each particle  size fraction  (to determine the fractional
penetration) and then used to calculate  the stage fractional
efficiency.  Percent efficiency versus particle size  (as particle
                                61

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   A.C. FINE TEST DUST
   O D INITIAL TESTS
   AC FINAL TESTS
     X HCSS DATA POINTS
                                        SIZE DISTRIBUTION
                                        AFTER SECOND STAGE
SIZE DISTRIBUTION
AFTER CYCLONE
                                           TEST AEROSOL
                                           SIZE DISTRIBUTION
                                       HCSS DUST LOADING, grams
                                         STAGE 1
                                         STAGE 2
                                         CYCLONE
                                         FILTER
               1                        10
              AERODYNAMIC PARTICLE DIAMETER, Dp, nm

 Figure 7. Inlet and outlet size distribution measurements using AC fine
         test dust.
100
                            62

-------
 99.9
   99
 a
a
cs>
CO
til
  .90
   70
   50
o  30
   10
   0.1
\   I  I I  I I |        I     I

   A. C. COARSE TEST DUST
 O A* INITIAL TESTS
 V + 0 FINAL TESTS
     X HCSS DATA POINTS
       SIZE DISTRIBUTION
       AFTER CYCLONE
                                                            I   I  i ITl
                                         SIZE DISTRIBUTION
                                         AFTER SECOND STAGE
                                  TEST AEROSOL
                                  SIZE DISTRIBUTION
                                             HCSS DUST LOADING, grams _
                                               STAGE 1
                                               STAGE 2
                                               CYCLONE
                                               FILTER
                                             TOTAL
        I   I  I  i i
                               I   I   I  I  I I I
                                                  2.747
                                                  0.244
                                                  0.213
                                                  0.023
                                                  3.227

                                                    I  I  I  I  I I
                   1                         10
                 AERODYNAMIC PARTICLE DIAMETER, Dp, urn
                                                             100
    Figure 8.  Inlet and outlet size distribution measurements using AC coarse
             test dust.
                                 63

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aerodynamic diameter)  is  shown in Figure 9.  Monodisperse  aerosol
test data obtained  by  McFarland3  is also shown.  Similar data
for the AC Coarse Test Dust  is shown in Figure 10.

     The explanation for  the apparent difference in  the cyclone
particle size/collection  efficiency curves for the two test  dusts
is poor experimental accuracy due to low stage weight gain.
As many researchers have  found, determining particle size/ef-
ficiency data using impactor classified particle size fractions,
obtained before and after a  particle collection device, is very
difficult and serves to justify the need to run tests using  known
diameter monodisperse  aerosols.

SUMMARY AND CONCLUSIONS

     The Andersen Model HCSS high grain-loading impactor was
tested with polydisperse  mineral dust aerosols.  If  reentrain-
ment of dust had occurred after the accumulation of  a significant
quantity of dust by a  collection stage, the stage collection
efficiency would decrease and the amount of coarse particles
penetrating that stage would significantly increase.  Size dis-
tribution and concentration  measurements after a clean and dust-
loaded HCSS impactor  indicated no measurable reentrainment of
dust.  These tests  were run  with the HCSS impactor in a hori-
zontal position operating at a flow rate of 14.2 &pm (0.5  cfm),
IUU

*, 80
c
0)
OJ
a.
>"
i- 60
Z
UJ
o
E
U.
QJ
z
o
h-
O
UJ
Ij 20
0
U

I I

—





—



—


_ .


I I
0.1
I I I

















I I I
III Ur I I"! I I&T ".— I B
I












/
/ 	 /
J /
/
x
A



CYCLONE ~
EFFICIENCY I STAGE 2
T EFFICIENCY
/
/
/
A
/ / I —
/ /
jP //
III I I I I I I I I I I
1.0 10 30
                      AERODYNAMIC PARTICLE DIAMETER, Dp, ,um

        Figure 9. Particle size versus collection efficiency calculated from conventional
               impactor measurements using AC fine test dust (from McFarland^).
                                64

-------
   100
  I 80
  V
  a
  u.
  ID
    60
  O 40
  u
  LU
  O
  o
20
                                          I  I

                                 CYCLONE
                                 EFFICIENCY
                                          STAGE 2
                                          EFFICIENCY
                                          I
                                        I  I I II I
      0.1
                       1.0                     10

                AERODYNAMIC PARTICLE DIAMETER, Dp, jum
30
      Figure 10. Particle size versus collection efficiency calculated from conventional
              impactor measurements using AC coarse test dust (from McFarland^).

sampling isokinetically through a straight  sampling  inlet.  This
is considered to  be  a realistic test and certainly  indicates
that the unit performed as intended.  Aerosol  size distribution
plots determined  using  the HCSS collected particulate matter
were essentially  the same as determined by  the standard multi-
stage impactor, which used grease coated collection  surfaces  (see
Figures 7  and 8).   Tests run with the unit  in  a  vertical position
and with downward  flow  gave results comparable to the horizontal
position.  Tests  run with upward flow through  a  vertical unit
show somewhat higher measured penetrations.

     The HCSS is  recommended for aerosol size  distribution mea-
surement if  the aerosol mass concentration  is  in the range from
2 to 200 grams/m3  (1 to 100 grains/ft3); with  a  gas  stream of
almost any gas composition compatible with  type  316  stainless
steel; at  any gas  temperature up to 1500°F; and  at  any reasonable
gas pressure.  For  long time sampling (2 to 24 hours)  the HCSS
can be used  for sampling aerosol mass concentrations as low as
0.2 grams/m3  (0.1  grains/ft3).

     Particle reentrainment may be a problem  for certain aerosols
at flow rates of  28  £pm (1 cfm) or higher,  although  field tests
with a non-bouncy  aerosol did not indicate  a  problem.   McFarland,
Ortiz and  Bertch   reported that gravitational  settling within
the HCSS first stage will cause a shift  in  collection character-
istics at  flow rates below 7 &pm  (0.25 cfm).   The unit may be
                                65

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useful for sampling at these lower flow rates if the stage collec-
tion characteristics are determined.

     The HCSS has the ability to fill an important gap in the
size selective sampling of aerosols:  that of sampling high aerosol
mass concentration streams.  Inlets to particulate collection
devices, fugitive dust sources, pneumatic conveying lines, parti-
culate process streams, long time sampling applications, or use
as a particle size classifier are example areas for application
of the HCSS.

NOTE

     Since this report was prepared, several additional field
tests have been run on a very high concentration, large particle
size (si to 500 pm diameter)  industrial aerosol.  The larger
particles were sintered spheres with minimum adhesion properties.
Extremely high mass loadings in the first impactor stage were
obtained and a carryover of about 7% of the first stage catch
to the second stage was determined by a subsequent analysis.  The
carryover was fairly constant with first stage loading (from 5
to 25 grams) and particle size (over the 10 to 500 ym size range).
This is an extreme sampling condition and represents a worst
case example.  Because ^80% of the aerosol was caught on the
first stage, a 7% carryover to the second stage about doubled
the second stage catch and would have caused a significant error.
Some carryover from the second impactor stage was also determined
but was not considered significant.  If appreciable quantities of
100+ um particles of a solid, spherical shape exist in the sampled
gas stream, it is recommended that the second stage catch be checked
for reentrainment and a suitable correction made.

REFERENCES

1.   Smith, W.B., and R.R. Wilson, Jr.  Development and Laboratory
     Evaluation of a Five-Stage Cyclone System.  EPA-600/7-78-008,
     U.S. Environmental Protection Agency, Research Triangle
     Park, NC, 1978.

2.   McFarland, A.R., C.A. Ortiz, and R.W. Bertch, Jr.  A High
     Capacity Preseparator for Collecting Large Particles.  Atmos.
     Environ. 13:761, 1979.

3.   McFarland, A.R.  Laboratory Evaluation of Andersen Hi-Capacity
     Stack Sampler.  Unpublished engineering report prepared
     for Andersen Samplers, Inc., December, 1978.

4.   Wright, B.M.  A New Dust Feed Mechanism.  J. Sci. Instrum.
     27:12, 1950.
                               66

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                              PAPER 4
        VELOCIMETRIC DETERMINATION OF AERODYNAMIC DIAMETER
                 IN THE RANGE FROM 0.1 ym TO 15 ym
                          JAMES C.  WILSON
                         BENJAMIN Y.H.  LIU
                  PARTICLE TECHNOLOGY LABORATORY
                 MECHANICAL ENGINEERING DEPARTMENT
                      UNIVERSITY OF MINNESOTA
ABSTRACT
     A technique for determining the aerodynamic diameter of
aerosol particles is described.  Particles are accelerated in
a nozzle, and their velocity is measured near the nozzle exit.
Careful choice of nozzle geometry and flow rate permits aerodynamic
diameter to be determined from the particle velocity.

     Experimental tests are reported in which velocity is mea-
sured with a laser-Doppler velocimeter.  Theoretical analysis
of the experimental tests shows that particle velocity can be
accurately predicted.

     Theoretical study of particle dynamics in the nozzle shows
that both aerodynamic diameter and density affect particle velo-
city if the motion is ultra-Stokesian.  This introduces uncer-
tainty in determination of aerodynamic diameter for such par-
ticles and provides an incentive for minimizing the particle
Reynolds number.

     Nozzle configurations and flow rates are proposed which
should permit determination of aerodynamic diameter in the fol-
lowing ranges:  0.1 ym to 1.5 ym, 0.5 ym to 10 ym, 1.5 ym to
15 ym, and 1 ym to 15 ym.

NOMENCLATURE

a    Radius of the nozzle at the exit

C    Slip correction

C    Drag coefficient

d    Distance from nozzle exit to point of measurement
                               67

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d_   Fringe spacing
D    Aerodynamic diameter
 a
D    Particle diameter
 P
AD   Diameter interval
f    Doppler frequency
F,    Body force acting on a particle
F,   Drag force acting on a particle
g    Gravitational acceleration
m    Particle mass
P    Pressure upstream of the nozzle
AP   Pressure drop across the nozzle
r    Radius of trajectory of particle executing curved motion
R    Radius of nozzle at position x
Re   Reynolds number, based on D
Re   Particle Reynolds number
St   Stokes number
t    Time
U    Gas velocity at exit of the nozzle
U    Gas velocity
 9
U *  Dimensionless gas velocity
U    Particle velocity
U *  Dimensionless particle velocity
U    Geometric mean particle velocity
 pg
U    Terminal velocity of particle settling under gravity
x    Position along centerline of nozzle axis
a    Angle of convergence of the nozzle
                              68

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X    Wavelength of laser radiation

y    Viscosity of gas

p    Density of the gas

p    Density of the particle

o    Geometric standard deviation of size distribution

0    Geometric standard deviation of velocity distribution

T    Period of Doppler signal

w    Angular velocity of a particle in curved motion

INTRODUCTION

     Aerodynamic diameter is an important measure of the size
of aerosol particles.  It is a single parameter combining par-
ticle density, diameter, shape factor, and slip correction, and
is used to predict the motion of particles in settling, impac-
tion, or in a centrifugal force field.  These motions frequently
cause particle deposition in the respiratory tract and particle
collection in gas cleaning devices such as cyclones and settling
chambers.  Consequently, it is often desirable to make accurate
measurements of aerodynamic diameter in order to study and pre-
dict these phenomena.

     The popularity of cascade impactors, cyclones, and impingers
is due in part to the fact that they measure aerodynamic diam-
eter.  However, these devices separate the particles from the
suspending gas, and their use often involves time-consuming
analysis of the collected particles.

     This paper describes a new instrument which allows rapid,
in-situ measurement of aerodynamic diameter.  The instrument
makes use of a nozzle to accelerate the particles and a laser-
Doppler velocimeter to measure the particle velocity near the
nozzle exit, as shown in Figure 1.

     Small particles are able to follow the flow as it accele-
rates rapidly in the nozzle.  Such particles emerge from the
nozzle with velocities near that of the gas.  Large particles
lag behind the gas flow and emerge with lower velocities.  The
velocity of individual particles emerging from the nozzle can
be measured by a laser-Doppler velocimeter.  In this system,
the laser beam is split and the two coherent beams are focused
by the transmitting optics to a crossover point where they form
interference fringes.  A particle passing through the fringes
scatters light, and the scattered intensity rises and falls as
                              69

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                             AEROSOL
                                ,CLEAN AIR
           LASER
 BEAM
SPLITTER
                                                PHOTOMULTIPLIER
                                                 WITH PREAMP
                                                OSCILLOSCOPE

             Figure 1. Schematic of the laser-Doppler velocimeter system.

the particle passes  through the  bright and dark bands.   The
scattered light  is collected and focused on a photomultiplier
tube  (PMT),  and  the  frequency of the intensity modulation  is
counted.  The particle  velocity  perpendicular to the  fringes
equals this  Doppler  frequency, fv, multiplied by the  fringe
spacing, df, which is calculated from the wavelength  of  the  laser
radiation and the angle between  the beams.  By choosing  appro-
priate nozzle parameters and flow rates, the aerodynamic diameter
can be determined from  the measured particle velocity.

     Other methods of determining particle size from  particle
velocity are reviewed elsewhere.

THEORETICAL  CONSIDERATIONS

Aerodynamic  Diameter

     The definition  of  aerodynamic diameter and its role in  de-
termining particle motion strongly affect the design  of  this
instrument.  Aerodynamic diameter is often defined as the  diam-
eter of a unit density  sphere with the same settling  velocity
as the particle  in question.2  The usual mathematical expression
for aerodynamic  diameter is derived here by considering  the
motion of particles  which settle with small values of the  par-
ticle Reynolds number.

     Equation 1  is the  equation  of particle motion and Equation 2
is Stokes law.
                  aS    ^
                •at*'*
                                                (1)
                Fd  =
(0
q
- u )
p
3
TT
P
D
P
                                                (2)
                                70

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Stokes law accurately describes the drag force on a spherical
particle moving with a Reynolds number, Rep, less than about
0.5, where

                     |U  - U I p D
                   -   "         P
     In the case of a particle settling in still air under gravity,
Ua = 0 and Fu, = mg.  The terminal velocity, Ut, is reached when
tne drag force equals the weight.  Thus, for a particle settling
in Stokes regime  (i.e., Re  <0.5),


                    C D 2 p g

               ut = —fe—

Since D , the aerodynamic diameter, is the diameter of the unit
density sphere having the same Ut as the particle in question,
D_ can be calculated as follows:
 Cl
                                   )Pp]   Dp .                   (5)


Non-spherical particles are treated by including the dynamic
shape factor.3' **

     Equation 5 does not follow from the settling velocity defini-
tion if the settling occurs outside of Stokes regime, as  is often
the case for large particles.  However, even in such cases, Equa-
tion 5 is taken as the definition of aerodynamic diameter because
Dg is useful in predicting other motions of the particle  which
may occur in Stokes regime.  For example,  consider impaction
(FL = 0) and centrifugal motion (F^ = mru)2) .  Combining Equa-
tions 1 and 2 with the appropriate expression for Fb results
in an equation which can be written in terms of Da and solved
for the particle trajectory.  Thus, for given flow field  and
initial conditions, the particle trajectory in an impactor or
cyclone is determined by Da if the motion  is Stokesian.   This
is true whether or not the particle settles in Stokes regime.

The Present Technique

     In the method described here, Da is determined by accele-
rating the particle in a converging nozzle  and measuring  its
velocity near the nozzle exit.  Appropriate flow conditions must
be chosen if Da is to be accurately determined from the particle
velocity.  Dimensional analysis of the equations of motion indi-
cates the factors involved in the choice.
                               71

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     Consider a particle on the axis of  the nozzle  shown  in  Fig
ure 1.  Equation 1 describes the motion  of the particle where
Fb equals zero and F^ is expressed  in Equation 6.

                    TT p  (U  - U ) 2  D 2 C

                  - ~^—a -     P    °
                a   ~          e

CD is the drag coefficient.  For Rep  <0.5, Stokes'  law  is  ex-
pressed as

               CD = 24/Rep  .                                   (7)


For 0.5 < ReD < 100, Fuchs3 suggests  the following  expression
for CD:

Equations 1 and 6 are combined and written in dimensionless form
to produce Equation 9,

               dU *   Re  (U * - U *)2C
                                 2 - D                        {9)
               dx*         24(St)U *
                                  P

where St is the Stokes number
and
               St  = C D 2 p  U /18 M a                       (10)
                        p   p  e
               Re = Ue Dp p/y .                               (11)
U  is the centerline gas velocity at the nozzle exit and  a  is
the nozzle exit radius.  Also,

               U * = U /U                                     (12)
                g     g  e


               V = V°e                                    (13)

                x* = x/a                                      (14)

and

               Re  = Re  (U * - U *)  .                         (15)
                               72

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     Substitution of Equations 7 and 15  into  9  shows that Up*
at a given point  depends upon St for motion in  which Rep <0.5.
Thus, for motion  in Stokes regime, St, and hence,  Da,  can be
determined from Up*.   In cases where Rep  >0.5,  the use of Equa-
tion 8  implies that Up* depends upon Re as well as St.  Thus,
particle  velocity depends upon the product of ppC, as  well as
Da, when  Rep  is large.   Therefore, particles  with  the  same ve-
locity  may nave different values of Da if they  have different
densities.  This  introduces an uncertainty in the  determination
of Da from Up* when p1  is unknown and Rep is  large.   This un-
certainty is  minimized  in this method by minimizing gas velocity,
and hence, Rep.   This distinguishes the present method from those
which employ  nozzles operating at large values  of  pressure drop.

EXPERIMENTAL  TEST

     Measurements were  made of the velocity of  particles emerging
from a  nozzle.  Particle size and flow through  the nozzle were
varied.   The  experimental system is diagrammed  in  Figure 2.
The actual test nozzle  was 1.77 cm in length and had entrance
and exit  diameters of 1.05 cm and 0.106 cm, respectively.   A
short throat  was  found  near the nozzle exit.  The  pressure across
the nozzle was varied between 2.54 cm H20 and 691  cm H20.   Sheath
air was used  to confine the aerosol near to the  center stream-
line.

     Monodisperse aerosols were generated from  PSL and PVT sus-
pensions, as  well as  with a vibrating orifice aerosol  generator.
The velocity  of individual particles was measured  with a laser-
Doppler velocimeter using a He-Ne laser.   A fringe spacing of

                                     SIGNAL PROCESSING
                                           _L
                   AEROSOL
                  GENERATOR
OL
1
INLET
PRESSURE
11
V 1
U

1
H
1 	
| PHOTOMULTIPLIER
o
1 r
M
^h
CHAMBER
(?) PRESSURE
' *• PUMP
                COMPRESSED AIR
                   FILTER
                          AEROSOL'
                          FLOWMETER
           COMPRESSED
             AIR
                                             ,  BEAM
                                             I SPLITTER
                                             LASER
                              SHEATH AIR
                              FLOWMETER
                Figure 2. Experimental system for the test nozzle.
                                73

-------
15.9 ym was  used for particles  larger than 3 ym, and  a  15 mw
He-Ne laser  and 7.13 ym fringe  spacing was used for smaller par-
ticles.  The center of the measuring volume was approximately
145 ym from  the exit of the nozzle  and extended four  fringes
on either  side of this point.   Details of the experimental pro-
cedure and results are described  in detail elsewhere.1'5

     Each  experimental trial  resulted in a frequency  distribution
of velocities which is characterized by a geometric mean  velocity,
Upg, and a geometric standard deviation, agv.  The geometric
mean velocities are plotted as  a  function of particle size and
for two values of nozzle pressure drop in Figure 3.

     The resolution which could be  expected from this system
can be estimated from the values  of agv and the particle  velocity
vs. diameter curve.   6
o
i-
cr
&
                            \
                                 X
                          EK
                          B

                                           cm of H^O

                                          ""-•069.1
                                         £E3*
                    0  I  23456789 10 II  12
                          PARTICLE DIAMETER , p.m

         Figure 3. Experimental and theoretical particle velocity at a distance of
                145 urn from the nozzle exit as a function of particle diameter
                and pressure drop across the test nozzle.
                                74

-------
    TABLE  1.   SELECTED VALUES OF  agv AND CORRESPONDING  DIAMETER
         	INTERVALS FOR  THE TEST  NOZZLE	

                   AP = 25.4 cm H20              AP = 69.1 cm H20
Dp, ym             agv      ADp,  Vm              °gv      ADp, ym
0.
3.
9
5
04

1.
1.
1.
007
005
007
±0.
±0.
±0.
25
05
15
1.
1.
1.
02
006
008
±0.
±0.
±0.
19
06
13

If the test aerosols were truly monodisperse, ADp would provide
a good estimate of the resolution of the system.  In the present
case, the system resolution for larger particles is smaller than
ADp, since the actual width of the test aerosol size distribution
is significant compared to ADp.  For the submicron particles,
the slope of the velocity vs. diameter curve limits resolution
for small values of pressure drop, and the increase in agv, per-
haps due to turbulence, limits resolution at large values of
pressure drop.

TEST OF THE THEORY

     Theoretical calculations were made of particle velocity
in the test nozzle.  These values were compared with the experi-
mental results as a check on the theory.  The first step in the
calculation was to calculate the air velocity in the nozzle from
the pressure drop and the nozzle dimensions.  Some asymmetries
in the nozzle shape required that average values of radius be
determined at positions along the axis to allow an axisymmetric
representation of the nozzle.  The axisymmetric representation
of the nozzle exit region is outlined in Figure 4.

     The velocity of the air in the nozzle was calculated using
two methods.  Boundary layer calculations6'7 were used to deter-
mine the velocity at every point in the nozzle, and Bernoulli's
law applied to plug flow was used to calculate only centerline
velocities.  Both calculations were made for the constant prop-
erty fluid case.   (See reference 5 for details.)  The two methods
agreed quite well on the centerline velocity, as is shown in
Figure 4.  The boundary layer calculations also provided informa-
tion on the flow profile in the test nozzle.  The calculated
flow profiles suggest that even for the lowest pressure drop,
a sheath air flow equal to one-half of the total flow is adequate
to insure that all particles experience nearly the same flow
field.  Therefore, only the centerline velocities are used in
the calculations of particle velocity.
                               75

-------
                       PLUG FLOW
                       CALCULATION
                       BOUNDARY
                        LAYER    AP, cm of H_0
                       CALCULATION
                        0.8   1.0   1.2   1.4
                        POSITION ALONG AXIS , cm
       Figure 4. Air velocity on the centerline of the test nozzle calculated using
              the boundary-layer approximation and Bernoulli's law applied to plug
              flow.  The axisymmetric representation of the nozzle exit region is
              also shown.
     The  particle velocity  was calculated  using a Runge-Kutta
technique to solve Equation 1 with the  drag force described by
Equation  6 and the drag  coefficients described by Equations 7
and 8.  The particle velocity measurements were made  approxi-
mately  145 urn downstream of the nozzle  exit;  therefore,  the
integration was continued to this point.   The gas velocity was
assumed constant over  this  distance.  The  particle and  gas ve-
locities  were assumed  identical at the  entrance to the  nozzle.
The results of the calculations are shown  in Figure 3.

     Comparison of the experimental and theoretical values of
particle  velocity shows  good agreement.   The percent  mean devia-
tion between the measured and calculated values is on the order
of 1.1% for AP = 61.9  cm of H20.  At a  AP  = 276 cm of H20, the
incompressible flow assumption should begin to fail,  yet the
mean deviation between measured and calculated velocities is
only about 3%.
                                76

-------
MEASUREMENT OF AERODYNAMIC DIAMETER

     Measurement of aerodynamic diameter  by  this  technique re-
quires careful choice of nozzle and  flow  parameters.   These
parameters determine the resolution  of  the systems  (particularly
for smaller particles), the uncertainty introduced  by uncertain
density and the aerosol sample rate.  General  solutions  to the
dimensionless equation of motion were obtained to facilitate
these choices.  Figure 5 shows the generalized nozzle geometry
used in the investigation.  Three angles, a  =  15°,  30°,  and 45°,
were selected, and the dimensionless gas  velocity on  the center-
line of each nozzle was calculated using  Bernoulli's  law for
ideal, one-dimensional flow.  The gas velocity was  assumed to
be constant over the distance d from the  nozzle exit  to  the point
of measurement.

     Equation 9 was then solved numerically  to find the  dimen-
sionless particle velocity, Up*, for each nozzle  as a function
of St, Re, and d.  Figure 6 shows results for  a = 45° and
d = 0.2a.  Solution sets were obtained  for ;, = 15°, 30", and
45°, with d = 0, 0.2a, 0.4a, and 0.6a.5   In  the case  shown in
Figure 6, the principal change in dimensionless velocity occurs
between (St)% = 0.4 and (St)% = 4.   This  geometry,  then, should
allow approximately one decade in Da to be measured for  a given
flow rate.  To determine a calibration  curve,  the smallest aero-
dynamic diameter to be measured with this system  is assigned
a value of (St)35 equal to about 0.4.  This fixes  the  ratio of
Ue/a.  Choosing the total flow in the nozzle then determines
Ue and a.  The curves are calculated for  incompressible  flow
in the nozzle; therefore, the pressure  drop  across  the nozzle
must be small compared to the upstream  pressure.  Once Ue and
a are chosen, values of St, Re, and  Da  are determined from
Equations 10, 11, and 5 for particles with the desired densities.
Then Up* is determined from the curves  in Figure  6  and is plotted
against Da.
                         tana
        Figure 5. Nozzle shape and parameters used in the theoretical analysis.
                               77

-------
                     0.2 0.30.4 0.60,81.0   2.0 3.04.0 6.08.010  15
      Figure 6.  Dimension/ess particle velocity as a function of Re and (St)^2 for a
              nozzle having a = 450 and d =* 0.2a.
     Figures 7 and  8  show  curves of UD* vs.
"P •! f* 1 1 T" O f\   T VN W y^ 4- V%  ^»t -^^^^N<^   /^i  —  A d O
                                             Da obtained  from
           In both cases,  a =  45°,  a - 0.05 cm, and d/a  =  0.2.
However, Ue = 9500 cm/s  in the first case, and Ue = 1200 cm/s
in the second.
     The system  shown  in  Figure 1 should permit the measurement
of Da for atmospheric  aerosols in the range from 0.5 ym  to  10  ynu
For particles having Da larger than about 2 pm, an uncertainty
is introduced into  the determination of Da from Up* if particle
density is unknown.  This uncertainty increases with Da  and can
be reduced by reducing Ue,  as  is done in Figure 8.  Here, resolu-
tion is lost for  submicron  particles, and the sample rate is
reduced to a level  unsuitable  for atmospheric sampling;  however,
an even wider range of densities results in a smaller uncertainty
in Da.  Experimental tests  are required to determine the resolu-
tion for small particles  and the maximum suitable sample flow
rate.  However,  sample flow rates near 37 cm3/s and 4.7  cm3/s,
respectively, are expected  for the two cases.

     Different nozzle  and flow parameters result in the  curves
shown in Figure  9.  The nozzle exit diameter is sufficiently
large so that velocity measurement can take place very near the
exit, although the  value  of d  = 0 is an exaggeration.  Reducing
d/a moves the curves in Figure 6 to the left.  The aerosol  sample
flow rate in this case is estimated to be 500 cm3/s and  should
be sufficient to permit sampling of coarse particles in  the at-
mosphere.  The uncertainty  introduced by density variations be-
tween 1 and 4.5  g/cm3  is  limited to about ±5% if p  = 2  g/cm3
is chosen as the reference  curve.
                                78

-------
                                    0=0.05 cm
                                    d=0.01 cm
                                    Ue = 9500cm/s
                                    P= I atm
                          23456789
                          AERODYNAMIC DIAMETER ,
Figure 7. Calibration curve for a nozzle whose parameters were chosen to permit
         measurement of atmospheric aerosols in the 0.5 urn to 10 nm range.
         The sample flow rate would be approximately 37 cm^/s.
               i.o
o
>"
K
O
8
               0.9
             2 0.8
             UJ
             y 07
             H
             CC
             3.
               0.6
            V)
            u
            O
            V)
               05
              0.4-
              a3
a = 45°
o = 0.05cm
d=0.01 cm
Ue= I200cm/s
P=lotm
                                                    = 2g/cm3 -
                      I  I   I  I
                0  I  2  3  4  5  6  7 8  9 10 II 12 13  14 15  16 17
                           AERODYNAMIC  DIAMETER , ^m
 Figure 8. Calibration curve for a nozzle whose parameters were chosen to permit
          measurement of aerosols in the 1.5 pm to  15 nm range.  The sample
          flow rate would be approximately 4.7 cm^/s.
                                  79

-------
  1.0


*^09


tOfl

3
UJ
> 0.7
UJ
o
H C
tr
Q.
,0 0.5

UJ
_J
§0.4
                 so.:
                 o
                  0.2
                       -i—i—i—r
                                    o=. 0.29 cm
                                    d=0 cm
                                      3870cm/s
                                      1atm
                      I  2 3 4 5 6  7 8 9 10 II 12 13 14 15 16
                        AERODYNAMIC DIAMETER,^m

     Figure 9. Calibration curve for a nozzle whose parameters were chosen to permit
            measurement of particles in the range from 1.5 JU/T? to 15 pm.  The
            sample flow rate should be adequate to permit convenient sampling of
            coarse particles in the atmosphere.
     Measurement of Da between  0.1  and 1.5 ym may be accomplished
with a nozzle  operating at reduced  pressure.  In the case  shown
in Figure  10,  the pressure upstream of the nozzle is assumed
to be 0.5  atm.   This may be accomplished by passing the  aerosol
through  a  critical orifice upstream of the nozzle.  The  pressure
drop in  the  nozzle itself is about  0.16 of the upstream  pressure.
The values of  aerodynamic diameter  shown in Figure 10 were cal-
culated  for  1  atm pressure.  Experimental tests will be  required
to determine the effect of turbulence on the resolution  and the
suitable aerosol sample flow rate.   Aerodynamic diameter is not
often useful in predicting the  motion of particles having  diam-
eters of a few tenths of a micron.   For such particles,  diffusion
is often more  important than impaction.  However, measurements
of Da may  be as informative in  this size range as the conventional
measurements of optical diameter.

CONCLUSIONS

     A velocimetric technique for measuring aerodynamic  diameter
has been described.  The method involves accelerating particles
in a nozzle  and measuring their  velocity near the nozzle exit.
Nozzle geometries and flow rates have been proposed for  measure-
ment of  aerodynamic diameter in the following ranges:  0.1 ym
to 1.5 ym, 0.5 ym to 10 ym, 1.5 ym  to 15 ym, and 1 ym to 15 ym.
Uncertain  particle density introduces uncertainty in the measure-
ment for the larger particles in each range, and the smallest
                                 80

-------
                 1.0
              *.» 0.9
              5 0.8
              UJ
              > 0.7
              £0.6
              K
              <
              Q.
                0.5
              CO
              in
              UJ
              z 0.4
              O
                0.3
                0.2
                      I  I  I  I  I  i  I  I  I  I  i  I  i  i  i  i
                                a = 45°
                                a = 0.01cm
                                d= 0.004 cm.
                                U,= l.65 X 10 cm/s
                                P- 0.5 atm
                                          1g/cm3
                            p- 3g/cm3-
                    i  i  i  i
                              i  i  i  i  i
                                          /»= 2g/cm 3-
                                         j	i
                    .I .2 .3  4  .5  .6  .7  .8 .9  I.O I.I 12 I.3 1.4 1.5 1.6 1.7 1.8
                          AERODYNAMIC DIAMETER, /im AT STP

        Figure 10.  Calibration curve for a nozzle whose parameters were chosen to
                 permit measurement of particles in the 0.1 yjn to 1.5 pm range.
                 Pressure upstream of the nozzle is assumed to be 0.5 atm.

particles  in each  range  may be affected  by turbulence which de-
grades  resolution.  This approach allows aerodynamic  diameter
to be accurately measured  rapidly and in situ.

ACKNOWLEDGEMENTS

     This  work was completed under  a  contract, No.  EY-76-S-02-
1248, from the U.S. Energy Research and  Development Administra-
tion.   The laser-Doppler velocimeter  was loaned by  TSI,  Inc.,
St. Paul,  Minnesota.  This report is  Particle Technology Labora-
tory Publication No.  398.

REFERENCES
1.
2.
Wilson,  J.C., and B.Y.H.  Liu.  Aerodynamic Particle  Size
Measurement by Laser-Doppler Velocimetry.  To be  published
in J. Aerosol Sci.

International Commission  on Radiological Protection  Task
Group on Lung Dynamics.   Deposition  and Retention Models
for Internal Dosimetry  of Human Respiratory Tract.   Health
Phys. 12:173-207, 1966.
3.
Fuchs,  N.A.   The Mechanics of Aerosols.
New York,  1964.
Pergamon  Press,
                                 81

-------
4.    Raabe, O.G.   Aerosol Aerodynamic Size Conventions for In-
     ertial Sampler Calibration.   J. Air Pollut. Control Assoc.
     26:856-860,  1976.

5.    Wilson, J.C.   Aerodynamic Particle Size Measurement by Laser-
     Doppler Velocimetry.  Ph.D.  Thesis, University of Minnesota,
     Mechanical Engineering Department, Particle Technology
     Laboratory,  1978.

6.    Patankar,  S.V., and B.D. Spaulding.  Heat and Mass Transfer
     in Boundary Layers, 2nd Ed.   Intertext Books, London, 1970.

7.    Sparrow, E.M., B.R. Baliga,  and S.V. Patankar.  Heat Trans-
     fer and Fluid Flow Analysis  of Interrupted-Wall Channels,
     with Application of Heat Exchangers.  J. Heat Transfer,
     99 Series  C:4-ll, 1977.
                               82

-------
                              PAPER 5
              A  PROTOTYPE  PARTICULATE STACK SAMPLER
                    WITH SINGLE-CUT NOZZLE AND
             MICROCOMPUTER CALCULATING/DISPLAY SYSTEM
                           JOHN C.  ELDER
                       LARRY G. LITTLEFIELD
                         MARVIN I.  TILLERY
                 LOS ALAMOS SCIENTIFIC LABORATORY
                     UNIVERSITY OF CALIFORNIA
ABSTRACT
     A prototype particulate stack sampler  (PPSS) has been de-
veloped to improve on the existing EPA Method 5 sampling apparatus,
Its primary features are (1) higher sampling rate (56 2,/min) ;
(2) display (on demand) of all required variables and calculated
values by a microcomputer-based calculating and display system;
(3) continuous stack gas moisture determination;  (4) a virtual
impactor nozzle with 3 ym mass median diameter cutpoint which
collects fine and coarse particle fractions on separate glass
fiber filters; (5) a variable-area inlet to maintain isokinetic
sampling conditions; and (6) conversion to stainless steel com-
ponents from the glass specified by EPA Method 5.  The basic
sampling techniques of EPA Method 5 have been retained; however,
versatility in the form of optional in-stack filters and general
modernization of the stack sampler have been provided in the
prototype design.  Laboratory testing with monodisperse dye
aerosols has shown the present variable inlet, virtual impactor
nozzle to have a collection efficiency which is less than 77%
and significant wall losses.  This is primarily due to lack  of
symmetry in this rectangular jet impactor and short transition
lengths dictated by physical design constraints  (required passage
of the nozzle through a 7.6 cm (3 in) diameter stack port).
Electronic components have shown acceptable service in laboratory
testing although no field testing of the prototype under a broad
range of temperature, humidity, and S02 concentration has been
undertaken.
                                83

-------
INTRODUCTION

     The standard manual stack sampling method for particulates,
EPA Method 5,1 was reviewed to identify needed improvements.2
A prototype particulate stack sampler  (PPSS) incorporating the
more desirable improvements into a general purpose particulate
stack sampler has been developed.  Increasing the flow rate
(double the 28 &/min °f most Method 5 samplers commercially
available)  permits shorter sampling time, collection of a larger
sample, or greater sensitivity.  Other major improvements include:
electronic calculating/display of calculated variables such as
stack velocity, sample volume, and per cent of isokinetic sampling
conditions; electronic continuous readout instrumentation for
temperature, pressure, flow, and humidity; reduced weight in
individual packages; stainless steel surfaces contacting the
gas stream; improved structural strength to reduce breakage;
single-point particle size classification (3 pm aerodynamic
diameter) in the nozzle; and optional in-stack particulate filter
sampler to simplify sampling at low stack moisture conditions.
Development of a null-probe device that would greatly simplify
stack sampling was discontinued due to technical problems.

     It was not our intention to provide an all-purpose sampler
capable of particulate sampling under all environmental condi-
tions.  Design specifications that the PPSS will meet are com-
pared with typical Method 5 capabilities in Table 1.  Our ex-
perience in the early stages of the study and experience of others
has shown that not all the conditions encountered in particulate
stack sampling can be accommodated by a single sampler.  It was
therefore decided that the design specifications should accommo-
date the most common ranges of stack temperatures, pressures,
and humidities found in actual use.  Several options could also
be provided to allow sampling under special conditions outside
these design limits.  The PPSS will not, for example, be appli-
cable to high-temperature conditions in the typical incinerator
stack, or to the high-temperature, nearly saturated conditions
of the power plant stack at the outlet of a scrubber where drop-
lets interfere with particle size classification in the nozzle.

     SI or metric units have been incorporated into the PPSS
to replace the British system of engineering units commonly used
in existing samplers.  Consistency of  units is observed within
the PPSS, and external data, such as barometric pressure, are
entered  into  the calculating/display system in the proper units.

PROTOTYPE PARTICULATE STACK SAMPLER  (PPSS) COMPONENTS

     The PPSS is shown schematically in Figure 1 and photographi-
cally  in Figure 2.  The primary  components  are  (1) an  in-stack
variable-inlet, virtual impactor nozzle capable of  inertially
separating the particle size distribution into two  fractions
                                84

-------
           TABLE 1.  EPA METHOD 5 AND THE PPSS COMPARED
       Feature
                         Method 5
                                                       PPSS
Nozzle cutpoint

Maximum port diameter

Maximum weight/package

Sample flowrate

Material
Stack velocity measure-
  ment

Maximum stack tempera-
  ture with cooling
  without cooling

Maximum stack diameter
Maximum stack gas
  velocity

Maximum stack gas
  humidity

Particulate filters

Number of samples

Calculation/display
Probe washing
                  None
                  7.6 cm (3 in.)

                  Approximately 27 kg

                  28 2,/min

                  Pyrex glass

                  S-type pitot


                  1000°C
                  320°C

                  9 m (30 ft)

                  >22 m/s


                  Saturated

                  Note b

                  5C

                  Nomograph calculation;
                    display by dials,
                    inclined gauge

                  Required
2.5-3.5 um

7.6 cm (3 in.)

24 kga

56 Jl/min
Stainless steel

S-type pitot


Not applicable
320°C

6 m (20 ft)

22 m/s


Nearly saturated

Note b

3C

Digital display
  on demand  (by
  microcomputer)

Not required
  after nozzle
  characteris-
  tics are known.
Notes
   b.
   c.
Production model weight can probably be reduced
approximately 20%.

Both methods can be provided with either in-stack or
out-of-stack particulate filters.

Number includes samples requiring preweighing, handling,
and analysis by some method; i.e., filter containing
solid material washed from probe, main gas filter, bleed
gas filter, impinger volume, or desiccant weight.
                                85

-------
oo
      VARIABLE
      INLET
      NOZZLE
=(jT) 	 STACK 1
> i^-PITOT A
^— zr — ' 01 F
4
to-t-
rr-n 	 	 	 &
fEMP
R STACK AP
ED FLOW pJ
I
I 	
I-BEAM SUPPORT (f
J ^ PROBE
^AAAAAAAAAAAAA/V AAAAAA/^VWi
T 	 ; 	 L T 	 • 	 «•!
Y-U-T— — — ' 	 —ir-r=.
r NOZZLE INLET PROBE =
\ POSITIONING
' ROD
I
n:
TEMPERATURE
EXTERNAL TEMPERATURE ~^\
yWVNAAAAAAA/VvWy ^A^\AAA/VSf- 1
-j- 	 '•' '" 	 - - - / /
Is* / EXTENSION ' Pi
^COUPLING NOZZLE INLET
POSITION INDICA
> 	 r ~
y 	 ^o
/
\

TOR
-—
=
A
~]S>
/FILTER
0 .-.TEMP
rf]

JT
i
BLEI
FLO\
J 	
B
— V
XFILTER HOLDER
STACK
FLOW
                                                                                                          1
                                                 STACK
                                                 WALL
                             CONTROL MODULE
! PSYCHROMETER MODULE
       „._____..,
                                        EXTENSION
                                      HEATER CONTROL
                                                      .FILTER

r
UMBILICAL l_
1
STACK APJ-LAP
COMP| ' 	
r— IPITOTAP h-r
1
_ ,. ^. .

_1 __.
*


                                                                                                            IDRYERS
                                       Figure 1. Schematic diagram of the PPSS.

-------
00
                                          Figure 2. Overall arrangement of the PPSS modules.

-------
(single cut-point  capability),  (2) a straight, heated,  stainless
steel probe with  smooth  internal surfaces and an  extension to
provide up to  3-m  inside-stack  length,  (3) an insulated 200-mm-
diameter  filter holder,  (4)  a wet-bulb, dry-bulb  psychrometer,  (5)
dii-cuoled or  water-cooled desiccant dryer,  (6) electronic flow
metPrs, (7) carbon vane  rotary  pump, and  (8) electronic tempera-
ture and  pressure  instrumentation.

Variable-Inlet, Virtual  Impactor Nozzle

     The  variable-inlet,  virtual impactor nozzle,  shown in Fig-
ure 3, was designed to pass  through a 7.6 cm  (3 in)  stack port.
The rectangular virtual  impactor was originally proposed as a
versatile single cut-point sampler by Forney.3  Virtual impac-
tion was  expected  to provide the advantage of low particle re-
bound and minimal  wall losses.   Further, the rectangular shape
of the jet was compatible with  the proposed rectangular variable
area inlet.
                           •VIRTUAL CHAMBER
                                  -SEAL RINGS

                                     POSITIONING
                                        ROD
                   INLET
         Figure 3. Section of variable-inlet, virtual impactor nozzle (Mod. 3).
                                88

-------
     The nozzle was designed to separate gas borne particles
as follows:  the larger particles in the gas stream  intrude  into
a volume of relatively stagnant air and, being  unable  to  nego-
tiate a sharp turn at that point, proceed  to a  collection filter
within the nozzle; the smaller particles successfully  negotiate
the turn and proceed along the probe to the main  sample filter.
By selection of appropriate length of the  jet  (L), width  of  the
jet (W), separation between jet and virtual surface  (S),  virtual
chamber width (H), main flow (Qm) and bleed flow  (Qb), the nozzle
should provide separation of particles at  the desired  aerodynamic
diameter cutpoint.  The dimensions L, W, and S  and the two flow-
rates are maintained constant during a sampling run.   Isokinetic
conditions are maintained by adjusting the nozzle opening N
during the run by mechanical linkage from  outside the  stack.

     Four versions of the variable-inlet,  virtual impactor nozzle
were tested by sampling monodisperse dye aerosol produced using
the Berglund-Liu vibrating orifice aerosol generator.  The ver-
sion shown in Figure 3 was the final version.   Although it was
adjusted to optimum ratios of S/W and H/W  recommended  by  Forney
et al.,1* the nozzle displayed the relatively low collection  ef-
ficiencies and high wall losses, as shown  in Figure  4.  Peak
efficiency did not exceed 77% and exhibited an  even  lower effi-
ciency for aerosols as large as 14 ym mass median diameter.
This efficiency is total aerosol mass collected in the virtual
chamber (thimble filter plus chamber wall  losses) as a per cent
of total aerosol mass entering the nozzle.  Wall losses in the
nozzle, probe, and filter holder ranged from 34-72% with  par-
ticles near the cutpoint size showing the  highest losses.  Figure
4 shows, in less detail, the designs of the previous three vir-
tual impactor nozzles and the performance  characteristics of
each of these designs.  Mod 2 displayed performance  character-
istics comparable to those previously noted for Mod  3.  Figure 5
shows a photograph, provided by Professors Ravenhall and  Forney,
detailing flow patterns within a water model geometrically similar
to our Mod 3 nozzle.  Breakup of streamlines starting  before
the exit of the jet illustrates nonuniformity of flow  which would
promote loss to the walls, particularly at a point opposite  the
small particle exit.  Further work on this particular  version
is not anticipated at this time.  However, if additional  work
is planned, it is recommended that a symmetrical nozzle (circular
or annular in shape) without the constraint of  fitting through
a 7.6 cm port be considered.  Larger port clearance will  allow
adequate length for smooth transitions within the inlet and
nozzle and greater separation between the  inlet and  the flow
disturbances caused by the broad body of the nozzle.   Symmetry
will allow the main flow stream to exit in all  directions, there-
by eliminating crossover and end effects inherent in rectangular
impactors.
                               89

-------
          MOD 0
                                     MOD 1
O
   90
   80
   70
                I      '    I  '  1 ' I '  I


                 0. ct.c _ VIRTUAL CHAMBER MASS

                 /0 EFF ~ MASS ENTERING INLET    _
                                            MOD 2-
E  60

LL
111
   50

o
UJ
         MOD 3
O
O
   40
   30
   20
                                I.I.I
                2         4     6   8  10        20


               MASS MEDIAN DIAMETER, /j.m
MOD 2
                                                                 VIRTUAL CHAMBER

                                                                      SEAL RINGS
        POSITIONING

        ROD
                                                                  MODE 3
                     Figure 4. Test results of virtual impactor nozzle.
                                       90

-------

-------
Stack Velocity Measurement

     Stack velocity is determined  from S-type pitot differential
pressure as measured by  an  electronic  pressure transducer with
± 25 mm H?0 range.  A null-probe device (Figure 6)  which provided
static pressure taps internal  and  external to the nozzle was
evaluated.  The small differential pressure induced by velocity
imbalance was sensed by  a  ±  25 mm  H20  differential pressure trans-
ducer and was minimized  to  achieve isokinetic conditions.  The
difficulty with this technique is  sensing  the low differential
pressure required  to achieve 0.9 
-------
 Instrumentation to Monitor Sampling Conditions

      Instrumentation in the PPSS is capable of transmitting con-
 tinuous voltage signals for calculating and display purposes,
 which replace the mechanical and manual methods of flow, pres-
 sure, and moisture measurement now part of Method 5.  These
 instruments  were selected to perform with accuracy and precision
 at  least equivalent to that provided by Method 5 instrumentation.
 Field testing to establish their ruggedness has not been accomp-
 lished.   Instrumentation channels are listed in Table 2 and dis-
 cussed in the following sections.

      Flow metering—Since the particulate mass concentration
 is  desired in terms of dry gas volume at standard temperature
 and pressure, dry gas volume is measured and automatically con-
 verted to standard conditions according to perfect gas laws.
 The gas  stream is dried and filtered prior to entering the flow
 meter.   Additional correction is required if constituents of
 the gas  change from the calibration gas or if temperature or
 pressure of  the gas stream varies from calibration conditions.
 Gas analysis  prior to each particulate sampling run is required
 to  provide gas constants to determine mass flow meter correction.

      Two flow meter types, hot-wire and turbine,  were included
 in  the prototype to permit evaluation under field conditions
 since laboratory testing did not show a clear advantage of one
 type  over  the other.   Datametrics hot-wire mass flow meter Model
 1000.5B  was  used to meter  the bleed flow.   It is  compact and
 lightweight  and has been used successfully in other  areas of
 our laboratory.   The instrument is  supplied with  linearizing
 signal conditioning.   A turbine flowmeter  (Flow Technology Model
 FTC-8) was used to meter sample flowrate.   The advantage of
 the turbine  flowmeter over a hot-wire flow sensor is  its direct
 indication of flow volume  in the presence  of gases other than
 the components of  air.   Its output  does,  however,  require com-
 pensation  for temperature  and pressure changes.

      Flow  control  is  performed  by manual  adjustment  of needle
 valves in  the main flow stream  and  the bleed flow stream.  This
 adjustment is made infrequently since normal operation with the
 virtual  impactor  nozzle requires constant  flow.
     Moisture measurement—The PPSS contains a wet-bulb, dry-
bulb psychrometer for measuring water vapor content of  the  sample
gas stream.  Total moisture can also be determined by measuring
total weight change in the dryers.  The volume occupied by  water
vapor is required in the isokinetic calculation to correct  nozzle
inlet velocity, which is volumetric flowrate of wet gas divided
by probe nozzle cross-sectional area.  The psychrometer, shown
                               93

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              TABLE 2.   PPSS INSTRUMENTATION CHANNELS

Sensors
Stack temperature
Probe temperature
Extension temperature
Holder temperature
Dry-bulb temperature
Wet-bulb temperature
Sample flow tempera-
ture compensation
Stack velocity (pitot)
Flow meter pressure
corrected

Psychrometer pressure
corrected

Sample flow rate
Bleed flow rate
Elapsed time
Interval time
Range or Max
20-325°C
20-325°C
20-150°C
20-150°C
20-150°C
20-150°C
20-150°C
±34 mb
±340 mb

±340 mb

7-12xlO~V/s
1-3x10" V/s
0-99 min:
0-60 s
0-99 min:
0-60 s
Type
RTD3
RTD
RTD
Thermistor
Thermistor
Thermistor
Thermistor
Variable
reluctance
Variable
reluctance
Variable
reluctance
Turbine
Hot-wire
Digital
Digital
Signal
0-5 Vdc
0-5 Vdc
0-5 Vdc
0-5 Vdc
0-5 Vdc
0-5 Vdc
0-5 Vdc
±5 Vdc
±5 Vdc

±5 Vdc

0-5 Vdc
0-5 Vdc


Overall
Precision
±5°C
±5°C
±5°C
±1°C
±0.5°C
±0.5°C
±1°C
±0.5 mb
±5 mb

±5 mb

±0.2xlO~'*m3/s
±0.1xlO~V/s



  Resistance temperature detector.
in Figure 7, is located  immediately  behind  the sample filter
where temperature of the gas  stream  is  maintained above dew point,
The wick material is polyester, which  is  resistant to the acids
(primarily dilute sulfuric  acid)  encountered in some sampling
situations.  The wick  is fed  from a  water reservoir through a
stainless steel tube approaching  within 3 mm of the thermistor
thermometer from the downstream side.   Covering the feed tube
with the wick  adjusts  the  temperature  of the feedwater to ap-
proximately that of  the  wet bulb  and prevents cooling or heating
of the  wet-bulb thermistor  by the feedwater.
                                94

-------
                                                     METAL BOX
                                                      WET-BULB
                                                      THERMISTOR
   DISTILLED
   WATER
   SUPPLY
             SUPPLY
             TUBE
                                                      DRY-BULB
                                                      THERMISTOR
                                           AIR IN

              Figure 7, Arrangement of wet-bulb, dry-bulb psychrometer.

     The wet-bulb,  dry-bulb psychrometer may be used up  to  dew
points of  100°C  with reasonable accuracy (less than 5% maximum
error).  Other methods of moisture measurement such as cooled-
mirror dew-point devices, hygroscopic salt devices, and  semi-
conductor  devices are limited by maximum ambient temperature,
usually about  50°C.

     Pressure  measurement—Three pressure channels are required
in the PPSS:   pitot tube differential pressure (stack gas velo-
city) ; pressure  at  the psychrometer; and pressure at the flow
measurement  section to allow pressure compensation of flowrates.
Pressure within  the stack to allow calculation of total  stack
volumetric or  mass  discharge is measured occasionally by connect-
ing one leg  of the  pitot tube to one of the existing transducers.
The operating  ranges of these instruments are listed in  Table 2.
Datametrics  variable-reluctance, differential-pressure trans-
ducers with  miniaturized carrier demodulators which supply  dc
voltage to the calculating/display system were used to monitor
pressure.  These transducers are lightweight and have displayed
good stability.


     Temperature measurement—All temperatures except stack  tem-
perature,  probe  temperature, and extension temperature are  sensed
by Yellow  Springs Thermilinear  thermistors which show good  linearity
and response.  They  are delicate and must be potted with epoxy
to make them more rugged and resistant to acid.   The accuracy
of the measuring circuit is generally within ±0.2°C over the
range 0-93°C.  Stability appears adequate,  showing standard  devia-
                                95

-------
tion of 0.05°C on the difference between two thermistors  in an
oil bath.  This order of stability is required by psychrometric
calculation which is based on wet-bulb, dry-bulb depression.
Sensitivity of the thermistor circuit is set at 0.1 V/°C,  far
exceeding response of any thermocouple.

     Stack temperature, probe temperature, and extension  tempera-
ture sensors are resistance thermometers  (RTD)  (Yellow Springs
Platinum RTD 0-138 AX), which provide the additional  range re-
quired at these locations.

Calculating/Display System

     A calculating/display system  is an integral part of  the
PPSS.6  The system incorporates a microcomputer and microprocessor
to calculate stack volumetric flowrate, sample  flowrate,  iso-
kinetic ratio, and various temperature and pressure compensation
factors.  A block diagram of the system is shown in Figure 8.

     The system operates on 115-Vac, 60-Hz line power and retains
read-only  (program) memory in the  event of power loss.   It dis-
plays data in  large  (1.3-cm) liquid crystal  displays  (LCD) visible
in strong sunlight.   Isokinetic ratio  is  updated and  displayed
whenever other values are not demanded.  All other variables
are displayed  on demand  through the keyboard.   Separate  clocks
provide  elapsed time  and  interval  time capability  (interval  time
prompts move to new  sampling location).

     The National Semiconductor MM 57109 MOS/LSI number-oriented
microprocessor performs  the number  processing/calculation.  This
28-pin dual  in-line  package provides scientific calculator in-
structions  (key level language) with reverse polish  notation
entry.   The  capabilities  of this device  include all  of  the func-
tions available on  the Hewlett Packard HP-21 hand  calculator.
The Intel ASM  48 single-component  microcomputer performs data
sequencing computation processing  and  display  updating.

     The microcomputer is programmed in assembly language and
allows operation in  the  following  selected modes:

     a.  Load  constants  - allows loading  of  all constants specific
to the run  (i.e., barometric pressure, gas constants, etc.);

     b.  Profile -  allows velocity traverse  across the  stack
while calculating stack  velocity;

     c.  Static pressure - allows  stack  pressure  to  be  measured
using  the  transducer  usually  assigned  to  monitoring  psychrometer
pressure;

     d.  Main  -  starts  the  clocks  and  updating of  all calculated
var iables;

     e.  Main  pause - allows  temporary interruption  of the run
to  relocate  the  sampler  to  another port;  also accommodates mid-
run delays  for any  other reason.

                                96

-------
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-------
     Although interfacing the microcomputer with all analog
signals has been completed and all calculations checked for
accuracy, overall system errors over typical ranges of operation
remain to be determined.  The microcomputer has functioned with-
out failure since original debugging of its software.  Its opera-
tion is rapid, with maximum calculating time 7.5 sec for  updating
stack velocity.

Equipment and Structural Arrangement

     The vacuum pump selected for the PPSS is a Cast 1022 carbon
vane rotary pump, which provides 280 2,/min at 0 mmHg and  68  Jl/min
at -500 mmHg.  Maximum pressure drop in the PPSS is 415 mmHg
(100 mmHg occurring in the nozzle, 115 mmHg in the 200-mm filter
holder, and 200 mmHg in the dryer).  The Model 1022 pump  weighs
23.6 kg  (52 Ib) and is the heaviest component in the PPSS.   In
general, weight of any other major component is limited to about
14 kg  (31 Ib).

     The probe of the PPSS will be supported by an I-beam canti-
levered outward from the stack.  This arrangement, shown  in  its
basic form  in Figure 1, will be similar to Method 5 arrangement.
The probe is  clamped in two places by a trolley device which
straddles the filter holder.

     The sampling probe is a straight 2.32 cm ID tube of  type
304 stainless steel.  Total heated length  is 130 cm.  The probe
is heated in  the manner of EPA Method 5, controlled by separate
automatic controller, and  is provided with a cooling air  blower
for temperature reduction  to 120°C when sampling intermediate
temperature stacks.  The probe extension is about the same weight
and length  as the sampling probe and allows 3m  total length.

     Lightweight dryers containing silica  gel desiccant  are  pro-
vided  for both the main and bleed  streams.  The dryer  is  designed
for either  air or ice bath cooling.  Silica gel crystals  are
packed within stainless steel bellows tubing.   A change  in mass
of the dryer  can be used as a measure of total  moisture  in  the
sample gas  stream.  Recharging is  accomplished  by  replacement
of desiccant  or drying  in  a warm oven  (70CC) .
 SUMMARY AND  CONCLUSIONS

      A prototype  particulate stack sampler has been developed
 with  the  following  primary features:   (1)  nominal 56 Jl/min sampl-
 ing  flowrate,  (2)  electronic transducers for pressure, tempera-
 ture, flow,  and  humidity ratio,  (3)  stainless steel surfaces
 and  components  not  subject to breakage,  (4)  electronic calcu-
 lating/display  system providing  direct display of updated data
 such  as  stack velocity,  sample volume, and isokinetic ratio,
                                98

-------
 (5) single-point particle  size classification  in  the  nozzle,
 (6) continuous adjustability of nozzle  inlet area,  and  (7)  manage-
able weight of individual  components.   A wet-bulb,  dry-bulb
psychrometer provides continuous  indication of  moisture  content
of the gas stream.  The psychrometer  is a  particularly promising
device in the severe conditions of high temperature (95  to  100°C)
and high humidity  in which the device must operate.

     The variable  inlet, virtual  impactor  nozzle  has  potential
for well-characterized separation of  fine  and  coarse  particulate,
although versions  tested to date  have shown collection efficien-
cies which do not  exceed 77%, and high  wall losses.   A new  design
with symmetry in flow passages and less dimensional constraint
is recommended.

     In general, the PPSS  has the operating capability of the
existing Method 5  sampling train, has modernized  its  design,
and has eliminated the obvious problem  areas.   However,  field
demonstration of the prototype might  reveal other problems  in
the novel areas of the PPSS design.  The effect of  acid  on  the
psychrometer wick  and of presence of COif  SOa?  and  other contami-
nants on behavior  of the psychrometer is not known.   Also,  stain-
less steel surfaces in the PPSS may provide greater potential
for formation of sulfate aerosols than  in  the  glass components
of the Method 5 train.  Component ruggedness remains  to  be  proven
by field testing.
ACKNOWLEDGEMENTS

     We would like to acknowledge the assistance of the  following
personnel in developing the PPSS design:  Dwayne C. Ethridge,
LASL, and Professors Forney and Ravenhall of the University of
Illinois, Urbana-Champaign.

     This work was supported by the Environmental Protection
Agency and performed at the Los Alamos Scientific Laboratory
operated under the auspices of the U.S. Department of Energy,
Contract No. W-7405-ENG-36.

     Reference to a company or product name in this paper does
not imply approval or recommendation of the product by the Uni-
versity of California or the U.S. Department of Energy to the
exclusion of others that may be suitable.
                                99

-------
REFERENCES

 1.  Federal Register 36(247)(December 23, 1971).

 2.  Elder, J.C., M.I. Tillery, and H.J. Ettinger.  Evaluation
     of EPA Method 5 Probe Deposition and Filter Media Efficiency.
     Los Alamos Scientific Laboratory Report LA-6899 PR, August,
     1977.

 3.  Forney, L.J.  Aerosol Fractionator for Large-Scale Sampling.
     Rev. Sci. Instrum. 47 (10):1264-1269, October 1976.

 4.  Forney, L.J., D.G. Ravenhall, and D«S. Winn.  Aerosol  Im-
     pactors:  A Study of a Fluid Jet Impinging on a Void.  J.
     Appl. Phys. 49(4):2339-2345, April 1978.

 5.  Federal Register 41(187)  (September 24, 1976).

 6.  Ethridge, C.D., and L.G.  Littlefield.  Microcontroller for
     Exhaust-Stack Environmental Measurements.  Los Alamos  Scien-
     tific Laboratory Report LA-UR-79-968, June 1979.
                               100

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                              PAPER 6



         THE EFFECTS OF NOZZLE LOSSES  ON IMPACTOR SAMPLING
                          KENNETH  T.  KNAPP
             ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
              U.S.  ENVIRONMENTAL PROTECTION AGENCY-RTP


     When measuring the mass, size distribution, and other prop-
erties of aerosols, getting a representative sample to the mea-
suring device system is an absolute must for obtaining good data.
The retention of particles by any part of  the sampling system
can greatly bias the results.  With impactors and other particle
sizing devices, the retention by the nozzle may be particle de-
pendent and, therefore, completely change  the size distribution
obtained.  This problem has been addressed by Marple and Willeke1
and others2"1* but few data have been given.

     The retention in the nozzle and the probe in the  standard
stationary source standard particulate emission measurement
methods such as EPA Methods 5 and 17 does  not cause a problem
since the nozzle and probe catches are included in the sample.
However, this is not the case with the proposed inhalable par-
ticulate matter (IP) measurement method.   The IP standard is
to include all particulate material with an aerodynamic size
at ambient conditions of 15 ym or less.  The stationary source
IP emission measurement method must contain a 15 ym particle
size cut system.  The general approach is  to use a 15 ym cut
point preseparator on the nozzle end of the probes used in the
particulate mass measurement methods such  as EPA Method 5.  The
preseparator would remove the particles larger than 15 ym aerody-
namic size and allow the remaining particles to pass into the
collection system.

     Experiments were designed to test such a separation system.
The first set-up tested was the preseparator with a button-hook
nozzle, the nozzle type most often used with EPA Method 5 and
other types of source sampling trains, since these nozzles will
fit into the 3 or 4-inch ports most commonly available.  A back-
up filter was used for the collection of the various size and
type aerosols.  The efficiency of the preseparators was deter-
mined by comparing the amount of aerosol retained in the pre-
separator including the nozzle to the total amount of aerosol
                               101

-------
collected.  After overcoming problems in generating monodisperse
aerosols with aerodynamic diameters greater than 15 yin,. testing
began.  On the first test runs with monodisperse aerosols of
about 10 urn, the button-hook nozzles were found to collect more
material than the preseparators.  If these nozzles retained a
large amount of material in the size range less than 15 ym, then
they cannot oe used with the preseparators without introducing
serious errors in the IP measurement.  Before a decision on
whether the button-hook nozzles could be used with the IP method,
the extent of the retention of the aerosols smaller than 15 ym
by these nozzles needed to be studied.  Such a study was under-
taken with 3/16, 1/4, and 5/16-inch button-hook nozzles.  These
were chosen for the tests since they are the size nozzles most
often used in stationary source testing.  In addition, a 90°
bend 1/4-inch nozzle was used in some tests.

     Tests with laboratory generated monodisperse aerosols and
re-dispersed sized coal-fired power plant fly ash were made.
The monodisperse aerosols were methylene blue particles generated
by a vibrating orifice  (Berglund-Liu) aerosol generator.  The
aerodynamic size range covered with these aerosols was from about
3 ym to about 27 ym.  The coal-fired fly ash used was separated
into five narrow size range fractions which had mass median diam-
eters  (MMD) of 3.5, 5.8, 8, 16.5, and 26.7 ym.  The sized fly
ash fractions were re-dispersed by the aerosol generator of the
Stationary Source Simulator Facility  (SSSF) in which the nozzles
were tested.

     The results from several test runs with the %-inch button-
hook nozzle and the monodisperse aerosols are given in Table 1.

           TABLE 1.  RETENTION OF MONODISPERSE AEROSOLS
        	BY 1/4-INCH BUTTON-HOOK NOZZLE	

        Aerosol diameter, ym          %  in %-inch nozzle
3.
5.
9.
10.
11.
15.
16.
26.
3
5
3
5
6
1
3
7
27
53
79
901:
13*
8*
6
4
+
+
+
D
3
D
+
+
2a
3a
6a



ia
la

        a
          Average and  range of  3  runs
          Single  runs
                               102

-------
     The results  of runs with the three nozzle  sizes on  various
aerosols are given in Table  2.


                TABLE 2.  COMPARISON OF  RETENTION OF
            MONODISPERSE AEROSOLS  BY THREE  NOZZLE SIZES

Aerosol diameter, ym
6.4
9.3
10.5
11.6
12.8
13.9
15.1
18.6
21
24
3/16
21
53
22
2
1
4
5
11
6
2
1/4
48
79
90
12.7
12
22
8
3
4
3
5/16
0
46
54
59
75
68
47
51
45
22
     Figure 1 is a  plot of the  data given  in Table  2.
                                                Q3/16 INCH
                                                A 1/4 INCH
                                                O 5/16 INCH
               2   4   6   8   10   12   14   16   18   20   22  24

                      AEROSOL MASS MEDIAN DIAMETER, urn


           Figure 1. Retention of mondisperse aerosols by nozzles of three sizes.
                                 103

-------
     A comparison of the ^s-inch button-hook with a 90° bend  \-
inch nozzle was  made with monodisperse  aerosols of 13.9 jam diam-
eter.  The results were 22% retained  in the button-hook and  24%
in the 90° bend  nozzle thus indicating  no difference.

     The results from the fly ash  study are given in Table 3
and Figure 2.
             TABLE 3.   RETENTION OF FLY ASH BY  NOZZLES
                           OF THREE  SIZES


Aerosol MMD, ym
3.5
5.8
8
16.5
26.7

3/16
28
22
6
4
2
% in nozzle
1/4
27
42
33
6
4

5/16
16
14
41
29
26

     The  tests were for collection  periods of 10 minutes.   The
question  whether the nozzle collection would reach an  equilibrium
was considered and runs of different collection times  were made
with the  ^-inch button-hook nozzles.  The results of  these tests
are shown in Table 4.
  100


   90


   80


s?  70
z
ji  eo

ui
m  50
oc

j  40
N
N
i  30


   20


   10


   0
                  T
                                           A 3/16 INCH
                                           O 1/4 INCH
                                           O 5/16 INCH
                   I
                   4   6   8   10   12  14   16  18  20   22  24

                    FLY ASH FRACTION MASS MEDIAN DIAMETER, jum
                                                   26
                 Figure 2. Retention of fly ash by nozzles of three sizes.
                                 104

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              TABLE 4.  EFFECT OF COLLECTION TIME ON
        	RETENTION OF  FLY ASH BY I/4-INCH  NOZZLE


        Collection time, min                  % in nozzle

                  5                               44
                 10                               33
                 20                               48
                 30                               32
No major difference over the period tested was found.

     All of the above data are from runs where the flow rate
was about 0.014 m3/rnin  (Q.5 CFM) .  This is the flow rate at which
the preseparators and impactors operate most efficiently.  How-
ever, since some tests will be made at different flow rates,
a study of the effects of flow rate on nozzle retention was car-
ried out with the %-inch button-hook nozzles.  Three flow  rates
were chosen for the test:  the optimum flow rate for the pre-
separators and impactors being tested  (0.5 CFM); the upper limit
of efficient operation of the preseparators (0.75 CFM); and a
flow rate commonly used with EPA Method 5  (1 CFM).  The 1  CFM
flow rate is not recommended for the preseparators because at
this flow rate severe re-entrainment occurs resulting in the
preseparator passing large amounts of particles greater than
15 urn.  The results for tests at the three flow rates with an
aerosol of about 11 ym are given in Table  5.

             TABLE 5.  FLOW RATES VS RETENTION OF FLY
        	ASH BY 1/4-INCH NOZZLE	

        Flow rate, m3/min                     % in nozzle

         0.014 (0.5 CFM)                          20
         0.021 (0.75 CFM)                          4
         0.028 (0.99 CFM)                          1
     The results of these tests have shown that the button-hook
and 90° bend nozzles retain various amounts of the aerosols that
are drawn through them.  The amount retained depends on the
nozzle size, the aerosol size, and the flow rate.  The percent
collected in the nozzle remained fairly constant over a time
period up to 30 minutes and, therefore, the collection does not
appear to reach an equilibrium.  Thus, the possible use of pre-
conditioning is eliminated.
                               105

-------
     Because much of the aerosols retained in the nozzles should
be passed on through the preseparator and onto the filter or
other collection devices, the use of the button-hook or 90° nozzle
with the IP method will cause large and varied errors.  The
nozzle retention does not cause a problem with the standard sta-
tionary source standard particulate emission measurement methods,
such as EPA Methods 5 and 17, since the nozzle catch is included
in the total catch.  However, particle size measurements with
these types of nozzles will have serious errors.

ACKNOWLEDGEMENTS

     The author wishes to acknowledge the assistance given by
Donald Duke and Raymond Steward for the aerosol generation studies
and Thomas Ward for separating the fly ash.

REFERENCES

1.   Marple, V.A., and K. Willeke.  Impactor Design.  Atmos.
     Environ. 10:891-896, 1976.

2.   Lundgren. D., and S. Calvert.  Aerosol Sampling with a Side
     Port Probe.  Am. Ind. Hygiene Assoc. J.  28:208-215, 1967.

3.   Cheng, Y., and C. Wang.  Inertial Deposition of Particles
     in a Bend.  J. Aerosol Sci. 6:139-145, 1975.

4.   Crane, R.I., and R.L. Evans.  Inertial Deposition of Par-
     ticles in a Bent Pipe.  J. Aerosol Sci. 8:161-170, 1977.
                               106

-------
                             PAPER  7


                 DILUTION SOURCE SAMPLING  SYSTEM
                        ROBERT J.  HEINSOHN
                          JOHN W. DAVIS
                CENTER FOR AIR ENVIRONMENT STUDIES
                THE PENNSYLVANIA STATE UNIVERSITY

                               AND

                         KENNETH T.  KNAPP
          NATIONAL ENVIRONMENTAL RESEARCH LABORATORY-RTF
               U.S.  ENVIRONMENTAL PROTECTION AGENCY
ABSTRACT

     A source sampling system has been designed and  tested that
is lighter and easier to use than the conventional EPA Method 5
sampling systems.  The heart of the system  is an ejector pump
that uses dry air to simultaneously pump, cool, and  dilute a
sample of a process gas stream.  The sample  is treated as a minis-
cule plume and the particles are removed from the sample after
it has been cooled and diluted with dry air.

     Simultaneous, full-scale source certification tests were
run with the dilution sampling system and a  conventional EPA
Method 5 system.  The emission from a coal-fired steam boiler,
a glass melt tank equipped with an electrostatic precipitator,
and a lime kiln equipped with a fabric filter were tested.  Test
results reveal that:

     (a)  the dilution system was considerably easier to use;

     (b)  the particle mass concentrations obtained  with the
          dilution system were larger than those obtained with
          an EPA Method 5 system;

     (c)  the size distribution obtained with the dilution sys-
          tem contained submicron particles  not observed at stack
          conditions as measured with an in-stack impactor;

     (d)  the relative abundance of elements in particles ob-
          tained by the dilution sampling system was considerably
          different from that in comparably  sized particles
          obtained by the EPA Method 5 system.  No consistent
          trends could be determined.

                               107

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NOMENCLATURE

a,b               constants

c                 apparent concentration of a material per unit
 m'°              mass of particle at any time zero

c                 concentration of a material per unit surface
 s                area of particle

c , c             mass concentration of a material per unit volume
 v   v'e          of the carrier gas at any time t, or at such
                  time when no further transport occurs, i.e.,
                  its equilibrium value

D                 diffusion coefficient

D                 particle diameter

g                 acceleration of gravity

hf                enthalpy of vaporization

H                 effective stack height

m^, m             mass flow rate of dilution air, sample

M , M             molecular weight of air and sample
 cl   S

n                 number of particles per unit volume of carrier
                  gas

Pr, Pr'            Prandtl number

P., P , PQ, psat  pressure of supply air, diluted sample, control
 1                pressure, vapor saturation pressure

AP                pressure difference across the sample orifice
  S

Q                 emission source strength

Q , Q             volumetric flow rate of dilution air and gas
     s            sample

R                 gas constant

r                 dilution ratio  (Qd/Qs), each corrected to
                  standard conditions

Re                Reynolds number

s                 atmospheric stability parameter
                               108

-------
S                 degree of saturation

T,, T ,  T         temperature of dilution air, diluted sample,
 d   m   s        sample

T,                 boiling temperature of a liquid

t                 time

u                 wind speed

X                 mole fraction

x,y,z             spatial coordinates

a,B               constants

6                 potential temperature

K                 thermal conductivity

p  , p0            density of vapor and of the liquid
 v   &

a  , a             atmospheric dispersion coefficients
 Y   z
T                 time constant


INTRODUCTION


     An  inherent limitation  in  all contemporary  source sampling
systems  is their inability to obtain particles in  the state  they
will have when the plume mixes  with the atmosphere.  In-stack
devices  capture particles at stack gas temperature and gas com-
position and EPA Method 5 systems capture particles on filters
at 121°C and in impingers at 0°C.  In these cases  condensation,
adsorption, and agglomeration that occur  in the  plume do  not
occur in a similar fashion in the sample.  The need for a sampl-
ing system that will  enable operators to  capture particles that
represent those a plume transfers to the  atmosphere has long
been recognized and is the basis for a novel  source sampling
system reported in this paper.

      A  source  sampling  system with  dilution  (hereafter  abbreviated
 SSD)  has been  designed  that  treats  the  sampled gas as  a  miniscule
 plume and  removes  particles  after  the  sample  has been  diluted
 with  clean dry air.1"1*   The  purposes  of  this  paper are  to:

      (1)  describe  the  design and  operation  of the SSD  system;

      (2)  analyze  simultaneous  samples  taken  with  the  SSD system
           and  a conventional EPA Method  5 system;  and

      (3)  compare  the processes of  adsorption, condensation,
           and  agglomeration  in  the  SSD  system and  plume.

                               109

-------
DESIGN OF SSD SYSTEM

     The SSD system is shown schematically in Figure 1; it con-
sists of six components.

     1.  Probe;  (length 2.07 m; mass 4.14 kg) null reading iso-
kinetic nozzle, impactor preseparator, heated probe, 1.27 cm
(^-inch) inside diameter, 1.83 m (6 ft) long.

     2.  Pump and Filter Assembly;   (length 0.68 m; mass 7.26
kg) ball valve, sample orifice, heated enclosure, Dilution Ejector
Pump (DEP), filter holder.

     3.  Umbilical Cord;  dilution air line, 120 VAC control
cable,  null nozzle pressure lines,  sample orifice pressure lines,
thermocouple leads.

     4.  Control Unit;   (0.46 m x 0.33 m x 0.23 m; mass 20.3
kg) pressure transducer, pressure regulator, pressure gauges,
temperature controller, critical flow orifice, dilution air
filter.

     5.  Flow Measurement Unit;  (0.38 m x 0.30 m x 0.23 m; mass
7.3 kg) electronics for  indicating elapsed time, volumetric flow
rate, and volume of sample.

     6.  Dilution Air Cleaner and Dryer;   (0.79 m, 0.41 m, 0.40
m; mass 25.7 kg) filters to remove oil and foreign matter, re-
generative dryer to remove water vapor.

     Units 1 and 2 are fitted with a taper fitting and mounted
on a tripod for insertion into  the stack.  The Control Unit
houses all the necessary meters and valves for controlling the
flow of dilution air.  The Flow Measurement Unit consists of
power supplies and digital logic system for conditioning, inte-
grating, and storing the signals related to the sample volumetric
flow rate and elapsed time.  The Dilution Air Cleaner  and Dryer
cleans and dries air to  operate the system.  The unit  is located
on the ground, and the air is supplied to  it by plant  air service
or a portable air compressor.   The unit is composed of commercially
available equipment and  will not be discussed.

     Performance specifications for the SSD system are as follows:

     I)  Sample flow rate:  0.236 to  0.708 liter/s  (0,5  to 1.5
sofm) and is adjustable  so that isokinetic sampling conditions
can be achieved at the nozzle  inlet.

     2)  Sampling nozzles:  0.318 cm,  0.635 cm,  0.953  cm, and
1.270 cm (1/8  in., 1/4  in., 3/8 in.,  1/2  in.).

     3)  The gas sample  and dilution  air  are  completely  mixed
before the particles are removed by a  filter; the  temperature
of the mixture  is within 5°C of the atmospheric  temperature.

     4)  The entire apparatus  is easily cleaned.

                               110

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  IMPACTOR
  PRESEPARATOR
                       PROBE
                       ASSEMBLY
                               TAPER FITTING
                                                        PUMP&FILTER
                                                        ASSEMBLY
                                                  BALL VALVE
                                                           HEATED CANISTER
                           /
COMPRESSED
AIR IN,
                          HEATED SAMPLE
                          PROBE

                   NULL-READING ISOKINETIC
                   SAMPLING NOZZLE
                                                                                 I
                                                                                 I  DEP
                                                                                 I
                                UMBILICAL
                                                                SAMPLE
                   FLOW MEASUREMENT,
                   UNIT
                           FLOW, VOLUME |
                           SAMPLE TIME  T
                           READOUT      I
             r
             i
      AIR CLEANER AND DRYER
                          I	I


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ORIFICE

TRANSDUCER

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              =e—
                        Ar
  PRESSURE
|  REGULATOR

I
                                         si


                                      Pf.  T,
                                                                             .PRESSURE
                                                                            /REGULATOR
                                                                       47 mm FILTER
                                                                                         /TEMPERATURE
                                                                                          CONTROLLER
                                                                               -CONTROL
                                                                                UNIT
                                              -FILTER
                                 Figure 1. Schematic diagram of sampling system.

-------
     Dilution Ejector Pump—The  Dilution Ejector Pump (DEP) shown
in Figure 2 is the heart of the  system.   Sample gas is pumped
by a high velocity stream of  dry dilution air passing through
the annular space around the  sample  tube, transferring momentum
to the slower moving sample gas  stream.   The two streams mix
and achieve uniform conditions5"8 at the end of the mixing tube.
The diluted stream then passes  through a filter to remove par-
ticles.  The DEP was designed to use a minimum amount of air
to cool the sample yet keep it  above the dew point.  Figure 3
shows the "well mixed" sample temperature as a function of the
dilution ratio (on the basis  of  volume), inlet sample temperature,
and moisture content.  The SSD  system was designed to accommodate
dilution ratios of 10 to 15.

     Control of sample flow rate—Dilution air enters the Control
Unit, is regulated to a set pressure (Po), passes through a three-
way ball valve and an orifice and into the DEP.  The dilution
air filter assures that all the  particles collected on the DEP
filter are from the sample gas.   The pressure, Po, controls the
sample flow rate and is controlled by the pressure regulator.
The supply pressure is P^.  A three-way ball valve is used to
pass the dilution air to the  DEP (as shown)  or to a separate
calibration system.  The sample  mass flow rate  (ms) is controlled
by the mass flow rate of the  dilution air, m^.  Since the geo-
metry of the DEP is constant, the mass flow rate of the dilution
air is a function of the regulated pressure, PQ.  The pressure
of the mixed gas before the filter (P^)  affects the sample mass
flow rate, but as this pressure  changes only slightly as par-
ticles are collected on the filter,  the pressure, Po, is the
principal factor controlling  the sample flow rate.
      1. MIXING AND DILUTION CHAMBER
      2. NIPPLE
      3. SAMPLING TUBE
      4. SAMPLING TUBE POSITIONER
      5. MOUNTING PLATE
      6. TUBE TO MALE PIPE FITTING
      7. GASKET
               Figure 2. Scale drawing of the dilution ejector pump (DEP).
                               112

-------
     150
   o
   o
     120
     100
   00
   Q
   LU
   LL
   O
   UJ
   cc
   D
   cc
   UJ
   Q.
   5
   UJ
WATER VAPOR IN SAMPLE
18.9% BY VOLUME
                                  10    12    14    16
                  18
                                                             20
                          DILUTION RATIO, r
       Figure 3. Temperature and relative humidity of diluted sample vs. dilution
              ratio for dilution air at 27°C and relative humidity less than 10%.


      The  sample flow rate also depends on  the size of the nozzle
and  the length  of the probe.  Figure  4 is  a graph of sample volu-
metric flow  rate (Qs) and the dilution ratio (Qf3/Qs)  versus the
control pressure PQ.   For the BSD system,  accurate measurement
of dilution  volumetric flow rate  is  not  needed since the operator
adjusts it to achieve isokinetic  sampling  conditions and a diluted
sample temperature within 5°C of  atmospheric temperature.  It
is essential that the sample volumetric  flow rate be measured
accurately.

      Measurement of volumetric flow  rate and total volume of
sample—An electronic system is used  for measuring the total
volume of the sample  and the sample  volumetric flow rate, and
in displaying these values.   An orifice  (0.635 cm diameter)
mounted upstream of the DEP was used  to  measure the sample volu-
metric flow  rate.   The temperatures of the orifice housing and
probe were held at 93.3°C (200°F).  The  electronic signal is
generated by a  pressure transducer  (located in Control Unit)
that  senses  the difference in pressure across the orifice  (APS).
The  transducer  output is a 0.5 to 5.5 volt signal that is linearly
proportional to the differential pressure  of  0.0 to 38.1 cm H20
(0.0  to 15 inches  H20).
                                113

-------
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            CONTROL PRESSURE Po(N/m2) x 104
 Figure 4. Operating characteristics of the DEP using a glass fiber filter
       and different inlet nozzles.
     The volumetric flow rate of the sample,  Qs,  is proportional
to the square  root  of AFS, which is obtained  by passing the trans-
ducer output through a square root extractor.   The output volt-
age from the square root extractor indicates  the volumetric flow
rate that  is needed in the computation of  sampling velocity at
the nozzle.  Integrated with time this signal determines the
total gas  volume  of the sample.  The integration is achieved
by converting  the output voltage from the  square root extractor
to a series of pulses with an analog-to-frequency converter,
and then summing  these pulses with respect to time.  The total
number of  pulses  is counted, and displayed as the total volume
of the sampled gas.  In addition, the elapsed time is also dis-
played.  The display is a set of light emitting diodes  (LED's).
Figure 5 is a  schematic diagram of the entire electronic system.
                                 114

-------
Ul
                                                    COUNTING BOARD (VOLUME)

                                                    RESET
            TRANSDUCER
                                                                                                      I  1   1   i    I   i
                                 FREQUENCY
                                 GENERATOR
                  PROBE       INPUT BOARD
COUNTING BOARD (TIMES)
                                                                                                       MULTIPLEXER BOARD
                                              Figure 5. Block diagram electronic circuit.

-------
     Four counting channels are used, two for counting elapsed
time, and two for counting the sampled volume of gas.  Each
volume counting channel  is associated with one of  the time count-
ing channels.  The information stored in each set  (one volume/one
time channel) can be  initialized  to  zero by  a button.  In  the
field, one volume and  time set is  initialized to zero before
the test, while the other is  initialized to  zero after sampling
at each  traverse point.  One  LED  display indicates volume, and
one LED  display indicates elapsed  time.  A selector  switch deter-
mines which  set of information is  displayed:  volume and  time
for entire test or volume and time for that  traverse point.
     Calibration and cleaning system—By means of two ball valves,
the operator can withdraw a sample from the stack or can pass
clean dry air through the system at a desired rate so as to re-
move particles from the orifice and DEP or to check the calibra-
tion of the orifice.  The dislodged particles pass through the
system and are deposited on the filter.  Thus no particles are
lost during the cleaning and calibration operation which can
be performed without removing the probe from the stack.  The
numerical value of the sampled gas volume is electronically
stored prior to cleaning and calibration and can be recalled
once sampling has resumed.  If particles collect around the
orifice and change its discharge coefficient, it will be detected
by the calibration procedure.  To compensate for a change in
calibration, a "calibration adjust" potentiometer mounted on
the face of the flow measurement unit enables the operator to
adjust the recorded flow rate and to set it equal to the cali-
bration flow rate.

OPERATION IN THE FIELD

     In the field the sampling system is operated as follows:

     1.  A nozzle is selected such that the sample flow rate
will be between 0.0140 and 0.0425 normal m3/min.  (Q.5 to 1.5
scfm).   (If a null-reading nozzle is not used, an independent
S-type pitot must be attached to the sampling probe.)

     2.  With the ball valve closed, the probe is inserted  in
the stack.  The stack gas velocity then is determined.  The  three-
way valve is set and dilution pressure adjusted  to pass dilution
air through the DEP at a rate that will withdraw a sample at
the isokinetic sampling rate.

     3.  The ball valve is then opened allowing  the  sampled  gas
to flow through the orifice.  The dilution air flow  rate  is  read-
justed to maintain  isokinetic sampling.
                               116

-------
COMPARISON TESTS

     Several samples were taken simultaneously with  the  SSD
system and an EPA Method 5 sampling  train  from the following
sources:

     1)   Coal-fired, traveling grate  stoker, boiler  (tests  1-5);

     2)   Glass melting tank  (tests  6-11);

     3)   Lime kiln  (tests 12-14).


     In tests 1,  6, 7, and 12-14, simultaneous full-scale source
certification tests were conducted.  Tests 2-5 and 8-11 were
conducted to determine the size distribution and elemental analy-
sis of the particles.  In tests 2-5 particle size measurements
were made with an Andersen-2000, 8-stage, in-stack impactor and
the SSD system.   In tests 8-11 the size distributions were deter-
mined by scanning electron microscopy.  Table 1 shows the mass
concentrations that were obtained, Table 2 shows the size distri-
bution, and Table 3 shows the results of elemental analysis per-
formed by a scanning electron microscope and an X-ray spectro-
graph.   Since the scanning electron microscope has poor accuracy,
the ratio of the amount of the element in the SSD sample to that
in the in-stack sample was computed.
   TABLE 1.  COMPARISON OF THE MASS CONCENTRATION DETERMINED BY
      THE SSD SYSTEM WITH THAT DETERMINED BY METHOD 5 SYSTEM
Source
Test
                                  Loading  (mg/ncm)
 SSD
 EPA Method 5
with impingers
  EPA Method 5
without impingers
Coal
fired
boiler

Glass
melt
tank

Lime
kiln
 6

 7

12

13

14
495.6



 71.7

351.7

116.2

 99.4

139.0
    462.1



     45.8

    331.8

    126.6

     83.8

    140.3
      407.6



       38.9

      323.6

      111.0

       70.0

      123.6
                               117

-------
    TABLE  2.  MEAN DIAMETERS AND GEOMETRIC  STANDARD  DEVIATIONS
           OF PARTICLES OBTAINED WITH THE SSD SYSTEM AND
                       AN  IN-STACK  IMPACTOR
Source Test Sampling train
,•
2

In-stack

SSD
Coal

fired • 3

In-stack

SSD
boiler

4


5
-
Glass
melt 8
tank
In-stack

SSD
In-stack

SSD
In-stack

SSD
Dry gas
volume
(ncm)
0.335

1.902

0.262

1.376

0.295

1.351
0.312

1.389
0.192

1.000
Mean diameter
(Vim)
7.2

0.4

10.2

3.0

9.6

0.3
4.1

0.4
0.4

0.4
Geometric
standard
deviation
3.1

6.6

2.4

5.4

3.9

1.7
4.6

5.3
2.2

2.2
DISCUSSION OF RESULTS

     Apparatus—One of the primary assets of the SSD system is
its size and ease of operation.  The DEP is considerably lighter
and smaller than the mechanical pump in an EPA Method 5 system.
The SSD has no glassware, impingers, ice, or impinger box to
be carried to the sampling site.  With no impinger box, the SSD
system is also easier to install on a support mechanism, such
as a monorail.  The dilution air cleaner and dryer can be left
unattended on the ground.  The ball valve located after the probe
and before the sample flow orifice is a positive shut-off.  When
a large probe is used the ball valve may be beyond the catwalk
or roof and require the operator to reach over the railing.
If the valve cannot be reached, the system can be shut off by
bringing the dilution air pressure to zero.  This, however, is
not a positive shut-off.

     Deposition of particles in the sampling system—Deposition
of particles in the sampling system (probe, orifice and DEP)
proved to be less than what occurs in an EPA Method 5 system.
A "scalping cyclone"  (Andersen-2000 preseparator) was mounted
between the sampling nozzle and upstream end of the heated probe
and removed particles greater than approximately 10 pm.  Table 4
shows the percentage deposition in parts of the SSD system for
a number of tests.
                               118

-------
TABLE 3.  RELATIVE ABUNDANCE OF ELEMENTS IN THE PARTICLES
   OBTAINED BY THE SSD SYSTEM TO THAT ON THE PARTICLES
                    WITHIN  THE  STACK
Test No.
Impactor
stage
3
4
5
6
7
8
Back Up
, 2 Coal-Fired Boiler with Aluminum as Reference Element
Cut size
ym
SSD/In-
stack
6.95/6.65
4.80/4.50
3.10/3.00
2.05/1.98
1.05/0.96
0.61/0.60
0.42/0.40
Element
Na
Al Si S
1.09 1.
0.39 1.
0.15 1.
2.18 1.
1.65 1.
4.76 1.
1.44 1.
Test No.
,0 1.14 1.
,0 0.63 0.
,0 0.69 2.
,0 1.47 1.
,0 0.96 0.
,0 0.80 0.
,0 0.95 0.
34
96
02
46
35
30
24
9 Glass Melt
K
1.02
0.80
1.62
1.02
0.45
1.79
0.90
Tank
Ca Fe Zn
1.
0.
0.
1.
1.
0.
2.

59 0.88
49 0.69
98 2.41
57 0.77
59 0.40 0.0
50 0.08 0.0
00 0.67 4.51


Element
Dp (ym)
6.30
4.00
2.50
1.60
1.00
0.63

Background
1
1
1
1
1
1

.00
.00
.00
.00
.00
.00

Al
0
0
0
0
0
1
Test
.77
.88
.97
.89
.99
.00
No.
Si
0.62
0.94
1.01
1.00
1.02
0.92
S
1.38
1.16
0.96
0.88
0.66
K Ca
0
0
0
0
0
0
10 Glass Melt
.58 0
.83 0
.88 0
.91 0
.83 0
.87 0
Tank
.67
.92
.97
.84
.95
.74

Fe
0.92
0.93
1.03
0.97
1.02
0.99

Ti
0.72
0.99
1.03
1.08
0.94
0.81

Element
Dp (ym)
10.00
6.30
4.00
2.50
1.60
1.00
0.63

Background
1
1
1
1
1
1
1

.00
.00
.00
.00
.00
.00
.00


0
0
1
1
1
1
1
Test
Al
.50
.73
.06
.18
.00
.10
.09
No.
Si
1.71
0.18
1.22
1.16
1.02
1.00
1.10
S
1.50
2.70
0.59
0.50
0.68
1.02
1.30

0
0
1
1
0
1
0
11 Glass Melt
K
.71 0
.82 1
.10 1
.34 1
.98 0
.09 1
.95 0
Tank
Ca
.79
.14
.06
.38
.96
.07
.93

Fe
0.78
1.01
1.48
1.50
1.10
0.94
1.15

Ti
0.75
0.96
1.14
1.27
1.07
1.00
1.16

Element
Dp (ym)
10.00
6.30
4.00
2.50
1.60
1.00
0.63
0.40
Background
1
1
1
1
_i_
1
J_
1
1
.00
.00
.00
.00
.00
.00
.00

1
0
1
1
0
0
0
Al
.02
.88
.26
.27
.79
.50
.64
Si
1.18
0.82
1.60
0.65
1.17
0.47
0.83
S
1.49
0.46
1.50
0.73
1.04
0.37
0.32

0
0
0
0
0
0
0
K
.60 0
.57 0
.91 1
.88 1
.80 2
.51 1
.78 6
Ca
.20
.80
.14
.86
.29
.77
.53
Fe
1.02
0.82
1.35
0.35
0.14
0.24
0.22
Ti
0.96
1.51
4.20
0.87
1.02
0.56
1.03
                           119

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	TABLE 4.   DEPOSITION IN SSD SYSTEM (IN PERCENT)	

                                                        Nozzle
                              Filter and    DEP and  preseparator
Test No.       Source       filter housing  orifice    and probe
1
6
7
12
13
14
Power plant
Glass melt tank
Glass melt tank
Lime kiln
Lime kiln
Lime kiln
35.1
16.7
79.0
36.6
48.0
36.5
18.2
41.5
7.0
18.7
21.5
16.5
46.7
41.8
14.0
44.7
30.5
47.0

     In laboratory experiments a monodisperse aerosol of uranine
dye was drawn through the sampling system at a volumetric flow
rate of 28.32 normal liters per minute  (1 scfm).   It was shown  .
that

     (a)  the scalping cyclone has a cut size of approximately
5 ym and is capable of removing particles above 10 pm,

     (b)  deposition in the sampling nozzle and orifice meter
is never more than 10% of the sampled aerosol,

     (c)  deposition in the DEP is never more than 20% of the
sampled aerosol,

     (d)  the final filter is the principal agent removing par-
ticles  that leave the scalping cyclone.

     Water content of samples—One important difference between
the SSD system and an EPA Method 5 system is the procedure to
calculate the water content of the sample gas.  EPA Method 5
trains  condense the water vapor and measure the remaining volume
of gas  in a positive displacement meter.  The water content of
the sample gas is easily determined by measuring the water in
the impingers.  The SSD system measures the total volume of
sampled stack gas including the water vapor.  The SSD system
thus requires a separate procedure (such as EPA Method 4) to
determine the water content.

     Isokineticity is inherently easier to achieve in the SSD
system.  An EPA Method 5 train uses a pitot tube to measure the
stack gas velocity and the sample flow rate is adjusted to achieve
isokinetic conditions.  To calculate the sample volumetric flow
rate to achieve isokinetic conditions, the temperature and water
                               120

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 content of the gas  entering the nozzle must  be  known.   Since the
 sample gas flow  rate is measured after the water  vapor has been
 condensed, the water content must be assumed to calculate the
 velocity.  The SSD  system measures the actual volumetric flow
 rate before  condensation of water vapor and  the above  assumption
 does not have  to be made.

      Particle  size  distribution, mass concentration and elemental
 analysis—The  mass  concentration obtained by the  SSD system was
 on the average larger than that obtained by  the EPA Method 5
 system when  the  impinger catch was included  and even larger than
 when the impinger catch was not included.  From the coal-fired
 boiler exhaust,  the size distribution obtained  by the  SSD system
 contained a  peak at 0.5 ym that was not present in the sample
 obtained at  stack gas temperature.  Figure 6 is typical of the
 data taken for tests 2-5.  The results of the elemental analysis
 show no consistent  pattern.
    160 —
    140 —
    120 —
    100 —
 c.
Q
 01

TJ

•D
	— DILUTION SAMPLING SYSTEM

      IN-STACK IMPACTOR
                         0.5      1.0                 5.0

                             PARTICLE DIAMETER Dp((im)


                  Figure 6. Particle size distribution, Test No. 3.
                                             10.0
20.0
                                 121

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     It is believed that the mass concentration, size distribu-
tion, and elemental analysis are affected by condensation, adsorp-
tion, and agglomeration that occur when the process gas stream
mixes with air.  The processes of adsorption, condensation, and
agglomeration were not modeled in this research so that predic-
tions of the mass concentration, size distribution, and the par-
ticle composition cannot be made.  Rather, these processes will
be examined in the plume and for samples obtained with the SSD
system and an EPA Method 5 system.  The purpose of this examina-
tion is to show that while the behavior of the diluted sample
and the plume differ in a number of respects, samples obtained
with the SSD system are more representative of the plume  than
samples obtained by either EPA Method 5 or Method 17 systems.

     A plume rises because of its momentum and buoyancy.  In
plumes from combustion processes buoyancy is dominant.  The plume
rises until its density equals that of the surrounding atmosphere.
Since plumes from fossil fuel burners have molecular weights
that are approximately the same as air, the plume rises until
its temperature is essentially equal to the surrounding air,
whereupon the wind then carries the plume downwind where  it
expands laterally and vertically by turbulent diffusion.  The
concentration of species within the plume can be expressed by
the Gaussian plume equation,
cv =
   _ Q_
2irua a
    Y
exp - (
                             exp
    r
exp [  -
                                                 (Z+H)
                                                 —r-
                 (1)
The critical parameters in the expression are the diffusion co-
efficients tfy,az , which increase with downwind distance x and
the atmospheric instability.  From the above it can be seen that:

      (a)  at any downwind distance the species concentration
          is Gaussian with respect to the vertical  (z) and trans-
          verse (y) distances

      (b)  with respect to downwind distance the concentration
          decreases exponentially.

Particles in the plume that are transferred to the  atmosphere
need  to be characterized in terms of mass concentration, size
distribution, and chemical composition.

      The way the SSD sample mixes with dilution air and the way
the plume mixes with the atmosphere differ in at least three
respects:  (a) Reynolds number,  (b) time scale, and  (c) mixing
mechanism.

      (a)  Reynolds number.  The Reynolds numbers of plumes depend
on the  installation but values of 10,000 or larger  can be ex-
pected.  The Reynolds number of the sample as it enters the DEP
                               122

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is 1000 or less.  Thus not only are the Reynolds numbers  dif-
ferent, but the plume is turbulent while  the  sample  is  laminar.

      (b)  Time scale.  The rates at which the sample  and  plume
mix with air are also different.  The  sample  mixes with dilution
air with a time scale given by:

      time = DEP volume/volumetric flow rate * 0.5 sec.


The plume mixes with the atmosphere over  a time period  that  is
difficult to estimate.  Bosanquet9 suggested  that the time for
a buoyant plume to rise is 2.16 s"1 where  s is related  to the
potential temperature gradient iLi by
                               3z

                           ,g.  8 6                              , _.
                       s =   ~z                              (2)

For a weakly stable atmosphere, t is approximately 200  seconds.
Once  the plume ceases to rise it spreads  and  mixes slowly with
a time scale of the order of hours or  days.   Assuming a plume
enters the atmosphere at 300°C and that the atmospheric tempera-
ture  is 25°C, the cooling rate of the  plume and SSD sample are,

          plume:  (300 - 25)/200 = 1.83°C/sec

          SSD sample:  (93.5 - 25J/0.5 =  137°C/sec

Thus  the cooling rate for a plume is considerably slower  than
the cooling rate for the SSD sample.   The  mixing of the plume
with  the atmosphere is characterized by large  scale turbulent
eddies and a slow rate of change toward equilibrium, while for
the SSD sample mixing is characterized by  small scale turbulent
eddies and rapid changes toward equilibrium.

      (c)  Mixing mechanism.  After the plume  rises, it  is trans-
ported downwind.  All during this time it  expands and mixes  with
the atmosphere.  Momentum transfer with the atmosphere  is small
and the plume spreads by lateral diffusion.   The concentration
of species within the plume can be expressed  by Equation  1.
The sample on the other hand mixes with dilution air all  the
while the two streams are confined within  the  DEP.  The sample
and the coaxial stream of air mix by the  transfer of momentum.
The concentration of species within the two streams can be esti-
mated by various expressions obtained  from the literature of
ducted turbulent jets.5"7  The thermodynamic  path followed by
the species within the plume is different  from the path followed
within the sample.  The SSD sample quickly mixes with dilution
air and is nearly uniform in temperature  and  concentration as
it enters the filter.  The plume remains  distinct for a consider
able  time and mixing is gradual.
                               123

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     The significance of these differences must be  judged  by
examining how particles  in a process gas  stream change when the
stream  is cooled and diluted with air.  Particles within the
plume or sample change by any one or combination of  three  pro-
cesses:   (a) particles may combine by coagulation,  or their
surfaces may act as sites for  (b) condensation or  (c) adsorption.
To  study how well a sample obtained with  an  SSD system simulates
conditions within the plume it is necessary  to determine if these
three processes are affected by  the differences above.
     Coagulation.  The rate at which the concentration  (n) of
particles of a particular size decreases by coagulation is given
below.  (Similar expressions should also be written for smaller
particles that combine to form a new particle of the particular
size in question.  The net change in concentration will then be
the difference between the two rates.)  For a first estimate,
simply consider the rate of removal of particles of a certain
size ,


                    ^ = -kn2                                  (3)
                    dt

The coefficient  k depends on the size of the particles  but  it
is of the order  of 10~10 cn^sec"1.  Because k is small, and  n
is of the order  of 103 cm~3, coagulation is unimportant within
the sample  or  during  the buoyant rise of the plume.  During  the
long  period the  plume spreads and mixes with atmosphere there
is time for coagulation but this is somewhat compensated  for
by the low  values of  (n) brought on by dilution.

      Condensation.  An indication of  the likelihood  that  condensa-
tion  occurs is the degree of saturation for condensable species.
The degree  of  saturation  (S) is defined as

         species partial pressure at  a temperature Tm _
         species saturation partial pressure at a  temperature  Tm


      c - X  P
       "
          Psat

 If  the  value of  S  is  equal to or  above unity then condensation
 can be  expected.

      The  mole  fraction of species j  in the diluted sample is


                                                               (4)
 where  r  is  the  dilution ratio and Ms and Ma the sample and air
 molecular weight.   The  saturation partial pressure at a tempera-
 ture Tm  can be  computed from the Clausius-Clapeyron equation,

                                124

-------
assuming Trouton's rule
h£  = 10.5 R T.
 fg           b
                                                               (5)
in which the heat of, vaporization  (hfg) is assumed constant  and
estimated at the boiling temperature TT^) at one atmosphere  and
assuming that the vapor behaves as an  ideal gas and R  is  the
gas constant.  The relationship between the saturation pressure
at Tm and the boiling temperature T^ at one atmosphere can be
expressed as
   (1/Psat> =
                                                               (6)
If the sample and the dilution air are ideal gases with constant
specific heats and mixing is adiabatic, the temperature of  the
diluted sample Tm leaving the DEP can be written as
                         T  + r T,
                    T  = __s	d
                     m     (r + 1)

Thus the degree of saturation of species j is

               X.

          Sj = -^M

                  XM
                                                               (7)
                       exp
r + 1)     1_"|
s + rTa " TaJ
                                           (8)
     The saturation ratio is not easily computed  for  the plume.
During the plume's buoyant rise there is little mixing  but  con-
siderable cooling and during the downwind dispersion  of the plume
the reverse is true.  In addition, there are distinct concentra-
tion gradients in the spreading plume and hence the saturation
ratio will vary with respect to x, y, and z.  For these reasons
a direct comparison of the saturation ratio of the SSD  sample
and the plume is not possible.

     The rate at which condensation increases the diameter  of
a single drop is given by Fletcher10 as,
          D  dD
          G =
-f = G [S-l-g +^-] f (Re, Pr')
P Dp
Dp
pv
PL
Dh. 2 p M .
1 + fq KV a f
RT K f

(
(

Re
Re

, Pr
,Pr)

')

                           -1
                                                               (9)
                               125

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The constants a and b relate to the effect of surface tension
and presence of a solute and the function f  (Re, Pr) accounts
for convection heat transfer.  The numerical value of the func-
tion is close to unity.  Each particle in a population of small
particles grows in a similar manner, but as the condensing ma-
terial is removed from the vapor phase the degree of saturation
(S) decreases.  It will also change because of cooling and dilu-
tion.  To model condensation for a population of particles re-
quires one to know the rate of cooling, and the original particle
size distribution, mass concentration, and saturation ratio.
The computation is complex and was not performed for either the
plume or the SSD sample.   The solution is doubly difficult for
the plume since the degree of saturation (S)  and temperature
vary with respect to x, y, and z.

     While the rates of cooling and dilution in the SSD sample
and plume are not identical, the SSD system more closely approxi-
mates the plume than the EPA Method 5 system in which there is
no dilution and the EPA Method 17 system in which there is neither
cooling nor dilution.

     Adsorption.  If the diameter of the particle does not change
rapidly, the rate of change of the mass of an adsorbed species
is equal to the rate at which material diffuses from the gas
phase, viz.
          dc
            s
                   [c  - c   3
          dt  ~ *  il-v    v,ej                                 (10)

where cm o and cs  are the concentrations of a material per  unit
mass and surface area of the particle and where cv  refers to
the concentration  of the material per unit volume of gas.   The
constant K is the  mass transfer coefficient.  From  the theory
of adsorption, equilibrium conditions can be described by the
Freundlich equation, in which cv e  is the concentration of  the
material in the gas phase at equilibrium.


                    c    = p  a c P                           (11)
                     v,e    p    s

     The values of a and 6 depend on the molecular  species  in
question and the units that are chosen.  The quantity a is  pro-
portional to the temperature while  3 depends on the nature  of
the van der Waals  forces on the particle's surface.

     While the above expression was not solved for  the plume
or the SSD sample, it is possible to determine whether adsorp-
tion in the SSD sample is comparable to that which  occurs in
                               126

-------
 the  plume.   Values  of  3  are  in  general  integers larger than unity,
 Assume  for  discussion  purposes  that  g=2.0.   If  the particle does
 not  initially  contain  any  of the  adsorbate,  the surface concen-
 tration at  any time t  can  be expressed  as

                    c    - c  (t)
                       '6     S
                    c    + G(t)
                     s,e    s
where
=  2
T =  2K
                                                              (13)
The parameter T is a time constant, such that if the elapsed
time is equal to  T the surface concentration will be 47% of its
equilibrium value, or if equal to 2 T the surface concentration
will be equal to  75% of its equilibrium value.  The numerical
value of T depends on the mass transfer coefficient K, and the
absorbate mass concentration cv.  The value of T is not easy
to compute since  it depends on the fluid mechanics of mixing
within the DEP and the plume.  If T is considerably smaller than
the residence time of the SSD system, then the surface concentra-
tion will achieve its equilibrium value by the time the sample
leaves the SSD system.

     Filter accumulation error — Inherent in any filtration system
is the constant exposure of the collected particles to the gas
stream.  Particles collected early in the sampling period will
be exposed to the gas stream longer than those collected at the
end of the sampling period.  Errors which may occur will be
called accumulation errors.  If the processes of adsorption and
condensation are  completed before the sample passes through the
filter, then there will be no accumulation error and the col-
lected particles  will represent those in the sample stream.
If however this is not true, and the particles continue to adsorb
and, or condense  gas phase species, then the collected particles
will not be representative of those in the sample stream.

     An accumulation error may seriously affect studies in which
condensation in the source is being investigated, if the degree
of saturation at  the filter is near unity.  Under such conditions
condensable vapors in the gas will continually condense on all
particles collected up to that constant.  Such an integrative
effect will suggest condensation that graatly exaggerates what
actually occurs in the plume.

CONCLUSIONS

     A new source sampling system has been designed that is easier
to use than a conventional EPA Method 5 system.  The heart of
the system is a Dilution Ejector Pump (DEP)  that uses dry atmo-
spheric air to withdraw a sample from a process gas stream and
simultaneously dilute and cool it with atmospheric air.  Within
                              127

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the DEP the sample reaches equilibrium with the dilution air
in a way that replicates the way actual plumes reach equilibrium
with the atmosphere.  The particles in the sample are cooled
to approximately ambient temperature and are deposited on a filter
for analysis.

     Tests have been conducted in which source samples were simul-
taneously withdrawn by the dilution sampling system and an EPA
Method 5 system; tests were also made with the dilution sampling
system and an in-stack system.  Comparison of the particles ob-
tained by the three systems reveals the following.

     (1)  The dilution sampling system records larger particle
          mass concentrations than an EPA Method 5 system.

     (2)  The size distribution of the particles obtained with
          the dilution sampling system is different from that
          obtained with an in-stack impactor.  Depending on the
          combustion process, the sample obtained with the dilu-
          tion system indicates the presence of submicron par-
          ticles emitted to the atmosphere that are not present
          at stack gas temperature.

     (3)  The presence of various elements on, or in, the par-
          ticles is significantly affected by the techniques
          with which the sample is obtained.

ACKNOWLEDGEMENT

     This research was supported by Grant No. R803560 from the
Environmental Protection Agency administered through the Center
for Air Environment Studies of The Pennsylvania State University
(CAES No. 521-78).

REFERENCES

 1.  Heinsohn, R.J., J.W. Davis, G.W. Anderson, and E.A. Kopetz,
     Jr.  The Design and Performance of a Stack Sampling System
     with Dilution.  Paper No. 76-37.3, Annual Meeting, Air Pol-
     lution Control Association, 1976.

 2.  Heinsohn, R.J., J.G. Wehrman, J.W. Davis, and G.W. Anderson.
     A Comparison of the Particulate Matter Obtained Using a
     Dilution Sampling System and a Method 5 Sampling System.
     Paper No. 77-12.1, Annual Meeting, Air Pollution Control
     Association, 1977.

 3.  Heinsohn, R.J., and J.W. Davis.  Design of Stack Sampling
     System with Dilution.  Center for Air Environment Studies,
     Pennsylvania State University, Report No. 494-78, 1978.
                                128

-------
 4.  Wehrman, J.G., R.J. Heinsohn, J.W. Davis, and G.W. Anderson.
     Instruction Manual for a Stack Sampler with Dilution.  Center
     for Air Environment Studies, Pennsylvania State University,
     Report No. 477-77, 1978.

 5.  Hedges, K.R., and P.G. Hill.  Compressible Flow Ejectors.
     Part I-Development of a Finite Difference Flow Model.  Paper
     No. 74-FE-i, Annual Meeting, American Society of Mechanical
     Engineers, 1974.

 6.  Hedges, K.R., and P.G. Hill.  Compressible Flow Ejectors.
     Part II-Flow Measurements and Analysis.  Paper No. 74-FE-2,
     Annual Meeting, American Society of Mechanical Engineers,
     1974.

 7.  Razinsky, E., and J.A. Brighton.  Confined Jet Mixing for
     Nonseparating Conditions.  J. Basic Eng., Trans. ASME 93(4):
     333-347, 1971.

 8.  Hidy, G.M.,  and S.K.  Friedlander.  Vapor Condensation in
     the Mixing Zone of a Jet.  AIChE J. 10(1):115-124, 1964.

 9.  Slade, D.H., ed.  Meteorology and Atomic Energy, 1968.
     TID-24190, Environmental Science Services Administration,
     Silver Spring,  MD, July, 1968.   p 192.

10.  Fletcher, N.J.   The Physics of  Rainclouds.   Cambridge Uni-
     versity Press,  New York, 1969.   pp 122-136.
                             129

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                             PAPER  8
          AEROSOL CHARACTERIZATION WITH A QUARTZ CRYSTAL
                  MICROBALANCE CASCADE  IMPACTOR
                          DAVID C. WOODS
                   NASA LANGLEY RESEARCH CENTER

                                AND

                         RAYMOND L. CHUAN
                       BRUNSWICK CORPORATION
ABSTRACT
     A Quartz Crystal Microbalance (QCM) cascade impactor, de-
veloped by Chuan,1 has been used by NASA to obtain in-situ data
on size distribution, elemental composition, and morphology of
aerosol particles.  Aerosols in rocket exhaust plumes have been
characterized using the QCM, in which the data are used for de-
veloping dispersion models for predicting plume behavior as a
function of meteorology and for assessing the environmental im-
pact of the effluents.  Volcanic effluents have been measured
in the troposphere and characterized with the instrument to sup-
port studies leading to an understanding of the volcano's geology
and its contribution to atmospheric aerosols.  NASA has more
recently utilized the QCM to measure both upper tropospheric
and stratospheric aerosols.  In this paper a description of the
QCM is presented, including its integration with several aircraft
which have served as platforms.  Also a review of the above mea-
surement efforts is given and selected data are presented and
discussed.

INTRODUCTION

     An aerosol sensor, designed by Chuan,1 has been used exten-
sively in research at the NASA Langley Research Center  for ob-
taining data on a variety of aerosols.  The sensor, referred
to as a Quartz Crystal Microbalance  (QCM) cascade impactor, mea-
sures aerosol concentration and size distribution (mass concen-
tration as a function of particle diameter) in-situ.  It combines
the use of piezoelectric crystal microbalances for sensing mass
in real time with the technique of inertial impaction,  with a
                               130

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cascade of impactors for classifying aerosols by aerodynamic
size.  Other methods that have been used for measuring size
distributions and concentrations of aerosols in-situ include
collection by impaction with later laboratory analysis such as
weighing, counting, etc., and single particle light scattering.
All methods, while providing valuable information, have uncer-
tainties associated with their measuring techniques.  For ex-
ample, the aerosols collected by the impaction methods may under-
go changes and/or evaporation between the time and location of
collection and the time and location of analysis.  Thus, this
is not a truly in-situ method.  On the other hand, size informa-
tion obtained from light scattering measurements involves un-
certainties in the knowledge of refractive index and particle
geometry.  Since the QCM cascade impactor senses mass in real
time, the problems associated with aerosol changes or evaporation
are avoided and since the size is determined by inertial classi-
fication, refractive index is not a factor.  It should be ap-
preciated, however, that the aerodynamic size of a particle
depends on its geometry and mass density.  In some cases these
factors may be assumed with reasonable accuracy or may be deter-
mined by post-sampling analysis.  Thus, the QCM offers a com-
plementary approach to obtaining aerosol data while avoiding
some of the problems encountered with commonly used techniques.

     In addition to the size distribution and mass concentration
data, the size separated aerosol collections can be further ana-
lyzed in the laboratory using scanning electron microscopy  (SEM)
with energy dispersive x-ray analysis to determine elemental
composition and particle morphology.  These data are of parti-
cular interest to researchers involved in the studies of plumes
from power plants, rocket motors, volcanic eruptions, etc.  They
are also important to the understanding of the interplay between
the earth's aerosol layer and solar radiation, through scatter-
ing and absorption, which affects visibility and the earth's
radiation budget and thereby may affect global climate.

     We have used the QCM as an airborne sensor on several dif-
ferent aircraft to characterize aerosols in rocket exhaust plumes,
in volcanic eruption plumes and in the upper troposphere and
lower stratosphere at several global locations.  Size distri-
bution data and data on elemental composition and morphology
were obtained from each set of measurements.  We present herein
a brief description of the QCM sensor and its use on various
aircraft.  Some typical data are presented.


Instrument Description and Operation

     The airborne QCM sensor (shown in the photograph in Fig-
ure 1)  consists of ten impaction stages.   Starting with stage 1,
the particle diameters for which the impaction efficiency is
50% (50% cut points)  are:   25,  12.5, 6.4, 3.2, 1.6, 0.8, 0.4,
                               131

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Figure  7. The 10-stage QCM cascade impactor for airborne measurements.
                                132

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0.2, 0.1, and 0.05 micrometers  (urn)  for equivalent  spherical
particles with a mass density of  2 g/cm3.   The  impaction  surface
in each stage, instead of being an inactive collector  such  as
a glass plate, a microscope grid, or  filter paper,  as  is  used
with conventional  impactors, is an active piezoelectric crystal.
The crystal, usually coated with  a thin layer of grease to  impede
particle bounce, is a part of an  oscillating circuit which  senses
the mass of the impacted aerosol  by  the associated  change in
frequency.  Therefore, by continuously monitoring the  oscillator
frequency in each  stage, one can  determine  the  aerosol mass col-
lected as a function of particle  size.

     Because of the very high sensitivity of the piezoelectric
microbalance (of the order of 109 Hz/g) a volume flow  rate  of
only 240 mi/min is used for sampling  at altitudes below 3 km
where the total mass concentration is on the order  of  10  to
100 yg/m3. At altitudes above 3 km where the mass concentra-
tion is on the order of 1 yg/m3 the  volume  flow rate is 2 il/min.
When sampling in ambient air a sampling time of the order of
a few minutes is usually required for a sensible signal while
a sampling time of only several seconds is  required when  sampling
in highly concentrated plumes such as rocket exhaust plumes or
volcanic plumes.

     When the sensor is flown external to the aircraft (e.g.,
under the wing of  the Sabreliner  and  Queenaire, or  on  the side
of the P-3), it is placed in an aerodynamically-shaped housing
(shown in Figure 1) which protects the sensor and allows  air
to flow around the cascade maintaining the  sensor at ambient
temperature.  Isokinetic sampling at  the required flow rate is
obtained by a specially designed  inlet probe.   It consists  of
two diffusers in series, as shown schematically in  Figure 2.
The object is to decelerate the air  which enters the probe  at
the aircraft speed Uo  (approximately  40 m/sec to 200 m/sec  depend-
ing on aircraft and altitude) to  a speed Us which matches the
air speed entering the impactor.  Us  is equal to V/A,  where V
is the volume flow rate into the  impactor and A is  the area of
its inlet.  Since A is not very large  (typically about 0.3  cm2),
to decelerate the air from Uo to Us  in a single duct would  re-
quire that the probe inlet area be too small and it would be
impractical to handle.  The solution  is to  start with  a practical
probe inlet area, Ao, of the order of 0.1 cm2  (equivalent diam-
eter of about 0.3 cm); decelerate by  a factor of 10 to 20 along
a small divergence angle diffuser (included angle 15°, to assure
no flow separation); skim the core of the decelerated  flow  with
a sharp-lipped "skimmer" of area A2, which  is a small  fraction
of the plenum area Ai, and deliver it to the second diffuser.
The excess flow in the plenum of the first  diffuser is vented
out to the atmosphere at the truncated base  of  the  diffuser where
the base pressure,  p^, is sub-atmospheric.
                               133

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                                                     TANDEM DIFFUSER INLET
OJ
                                                                                                     STAGE 1
                                                                                  CASCADE HOUSING
                                                 Us = CASCADE INLET FLOW SPEED
                                                  V = (U0A0)
A2  *S
A1  A4
                                         Figure 2. A schematic of the airborne QCM inlet.

-------
     In the second diffuser the velocity U^  is again decelerated
by a factor of about 10, to match the  impactor inlet velocity,
Us, which for the case of V = 2000 m£/min and inlet area of  0.3
cm2 is about 100 cm/s  (as compared to  the airplane speed of  200
m/s, a factor of 200) .  The QCM inlet  acts as the core  "skimmer"
in the plenum of the second diffuser.  The excess flow  is  vented
out of the base of the second diffuser into  the housing which
is in turn vented through its base, at base  pressure, p^,  less
than ambient, into the atmosphere.

     The flow relationship through various stations along  the
tandem diffuser is shown below the schematic in Figure  2.  By
judicious selection of the various areas it  will be found  that
the impactor inlet can be readily matched to any specified flight
speed.

     In a typical sampling flight the  instrument is placed in
its standby mode, in which ambient air is taken through the  im-
pactor through a total filter while en route to the sampling
site.  Just before a plume is entered, the sampling valve  is
moved from the standby position to the sampling position and
the air flows directly into the impactor, bypassing the absolute
filter.  When the airplane leaves the  plume  (or when sufficient
signal is obtained in case one is flying along a long plume)
the valve is returned to standby.  The frequency change in each
stage and the time in the plume yields the aerosol mass concen-
tration in each stage.  These frequencies are recorded  by  a
printer in the instrument control unit, so that the raw data
can be analyzed after the flight.

     Table 1 summarizes the measurement efforts in which the
QCM cascade impactor has been utilized by the Langley Research
Center.  The geographical locations, the types of aerosols mea-
sured, and the aircraft used for the measurements are listed
in chronological order.  The following will  include discussions
on portions of selected experiments from this table.  These  dis-
cussions are intended to illustrate the kinds of experiments
in which the QCM may provide useful information and the results
that may be expected.

Solid Propellant Rocket Exhaust

     Our initial use of the QCM as an airborne sensor was  for
sampling and characterizing particulates in  the exhaust plumes
from solid propellant rocket motors (Deltas  and Titans)  at Ken-
nedy Space Center starting in 1974.  For the earlier measurements
we used a single stage QCM impactor2 which was a modification
of one previously used as a ground sampling  instrument.   It was
mounted in the forward baggage compartment of a Cessna 402 with
protruding isokinetic inlet probes supplying the sample to the
sensor.  The single stage impactor provided  mass concentration
data and no real-time particle size data.  It was replaced in
1977 by a 10-stage impactor which was  flown  in a rocket plume.3
                               135

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  Date
TABLE 1.  APPLICATIONS OF THE QCM CASCADE IMPACTOR AT LANGLEY RESEARCH CENTER	

                                                                           Approximate
                                                            Aircraft       Altitude  (km)
Location
Type of Measurement
May 77    Fairbanks, Alaska

May 77    KSC

Aug. 77   KSC

Sept. 77  KSC

Feb. 78   Guatemala
                        Stratospheric Aerosol

                        Rocket Effluents

                        Rocket Effluents

                        Rocket Effluents

                        Volcanic Effluents

                        Tropospheric Aerosol
Sept. 78  Laramie, Wyoming

Nov. 78   Sondrestrom, Greenland  Stratospheric Aerosol

Dec. 78   KSC                     Rocket Effluents

Mar. 79   Dallas, Texas           Tropospheric Aerosol

Apr. 79   Natal, Brazil           Tropospheric Aerosol

Apr. 79   St. Vincent Island      Volcanic Effluents (Soufriere)

May 79    St. Vincent Island      Volcanic Effluents (Soufriere)
                                                 NCAR Sabreliner       10-13

                                                 Cessna 402           0.3-2.0

                                                 Cessna 402           0.3-2.0

                                                 Cessna 402           0.3-2.0

                                                 NCAR Queenaire        ~5

                                                 NASA Wallops P-3       3-7.6

                                                 NCAR Sabreliner       10-13

                                                 Cessna 402           0.3-2.0

                                                 NASA Wallops P-3       3-7.6

                                                 NASA Wallops P-3       3-7.6

                                                 NASA Wallops P-3       3-7.6

                                                 NASA Wallops P-3       3-5

-------
      During  a  typical sampling  flight the aircraft made a series
 of passes  through the center  of the visible plume flying in a
 figure eight pattern while  at the same time changing altitude
 between passes.   Figure 3  (from data taken in  December 1978)
 shows a size distribution plot  of AC/AlogD  as a  function of
 D, where C is  the mass concentration in units  of  yg/m3, and D
 is the particle  diameter in micrometers.  The  bimodal distri-
 bution, typical  of rocket exhaust plumes, has  a sub-micron peak
 at O.l-jum  diameter and a second peak between 3.2  and 6.4 urn.
    70
    60
    50
    40
01
3.
o
I   30
o
   20
    10 -
                                   J_
                    0.1
     1.0

DIAMETER, j
10
100
       Figure 3. Particle size distribution in the exhaust plume from a Titan III rocket
              launched at Kennedy Space Center on December 13, 1978.
                                 137

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Aluminum oxide (A12O.,) spheres, formed by combustion of the
rocket propellant, have been found to make up the major portion
of the particulates in the large size moded as illustrated in
Figures 4a and 4b.  Figure 4a shows an SEM photograph of par-
ticles collected in stage 5 of the cascade impactor corresponding
to 1.6-ym diameter.  Figure 4b shows an x-ray energy mapping
for aluminum  (Al), where the bright spots indicate the presence
of Al.  These spots map into the particles in Figure 4a indi-
cating that they do contain Al.  Since they are spherical in
shape and show no other elements in the x-ray energy spectrum
they are presumed to be Al,03 particles.  In general, the par-
ticles in the 0.1-ym size mode are more complex, consisting of
single spherical A1203 particles, and agglomerates which contain
sodium, aluminum, sulfur, chlorine, potassium, calcium, iron
and zinc.3  It is suspected that the A1203 particles formed in
the exhaust cloud are formed by two processes thus producing
the bimodal distribution.  The spherical particles in the large
size mode are believed to be formed molten alumina and the ones
in the submicron size mode are believed to be formed from gas
phase condensation.

Stratospheric Aerosols

     In preparation for a series of intercomparative experiments
with the QCM  and several other types of aerosol sensors, the
QCM was recently integrated and test flown on the NASA Ames U-2
aircraft.  The U-2 is capable of reaching altitudes of greater
than 20 km.   The QCM, its control unit, and printer were mounted
inside an area on top of the fuselage.  A stainless steel inlet
probe protruding through a cover plate was used to provide the
sample air.   A single three-way control switch was provided in
the cockpit for the pilot to perform all operations.

     The following data were taken with the QCM aboard the U-2
during a photographic mission over south central California on
June 11, 1979.  The measurements were made during level flight
at an altitude of 19.8 km.  Figures 5a and 5b show plots of
AC/AlogD as a function of D, for two consecutive 10-minute in-
tervals.  These plots show again a bimodal characteristic in
mass concentration:  a weaker one at 0.2-ym diameter and a rela-
tively strong mode for the 1.6-ym diameter particles.  In addi-
tion, Figure  5a shows an indication of an increase in AC/AlogD
at 0.6 ym.

     The SEM  photograph in Figure 6 shows a sample of the par-
ticles collected in stage 8 of the cascade impactor correspond-
ing to the peak in the small size range of the bimodal distri-
bution.  The  majority of the particles appear to be nearly spheri-
cal in shape  and are on the order of about 0.2 ym in diameter,
which is the  50% cut point for stage 8.  There are quite a few
irregularly shaped larger particles, on the order of 0.5 to 1.0
micrometers.  These particles apparently have mass densities
lower than 2.0 g/cm3, the density for which the 50% collection
                               138

-------
Figure 4. (a)  Scanning electron microscope photograph of particles collected in
         stage 5 of the QCM cascade impactor for a Titan rocket exhaust plume.
         (b)  X-r
-------
     2.4
     2.0
n

 E

 01
 S1
     1.6
     1.2
     0.8
               \

                \/
              -tit
                                                                   /
                                                                   /
     0.4
     0.0
                                                   _L
                             0.1
     1.0


DIAMETER,/zm
10
                                                                                              100
           Figure 5a.   Size distribution plots of stratospheric aerosol particles measured with

                      the QCM in the NASA Ames U-2 aircraft at 19.8 km over south

                      central California.

-------
2.4  -
CO
 5
 S
 Q*
 o>
 O
2.0
1.6
1.2
0.8
                                     !     \   I
0.4
0.0
                                                 J_
                          0.1
                                                       1.0

                                                 DIAMETER,
                                                                        10
                                                                                                     100
      Figure 5b.  Size distribution plots of stratospheric aerosol particles measured with
                 the QCM in  the NASA Ames U-2 aircraft at 19.8 km over south
                 central California.

-------
6.  Scanning electron microscope photographs of stratospheric particles
   collected in stage 8 of the QCM cascade impactor over south central
   California at 19.8 km.
                             142

-------
efficiencies are determined.   The  combination of density and
shape causes these particles  to  behave  aerodynamically as if
they are 0.2-micrometer diameter spheres  with a mass density
of 2 g/cm3.

     Three of the particles  in Figure  6 were selected for energy
dispersive x-ray analysis, particles A, B,  and C.   Particle A
is approximately spherical but is  greater than 0.5 ym in diam-
eter.  B appears to have more of a cubic  shape and is on the
order of about the same size  as  A.  C,  on the other hand, is
much smaller than A and B, being on the order of about 0.2 ym
and spherical in shape.  The  type  C particles are much more
abundant than the other types.   The x-ray energy spectra for
the three particles are shown in Figure 7 along with a background
spectrum.  A and B show the  same elements while C shows no x-
ray spectrum at all, either  because of  its  small size or because
there are no elements present that can  be detected by this x-
ray method.  In general, it  was  found  that  the morphology of
the particles as well as the  composition  differed for the various
impaction stages, indicating  that  the  various types of particles
are size dependent.
         (A)
          (B)
           Figure 7. X-ray energy spectra for particles A, B, and C in Figure 6.
                               143

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Volcanic  Plumes

     The  QCM was aboard  the NCAR Queenaire when it made  a series
of sampling flights over  the active volcanoes, Fuego  and Santia-
guito  in  Guatemala, during  February and  March 1978. "*   During
the sampling period, Santiaguito was  producing several large
ash-laden eruption clouds per day, some  rising to higher than
5 km above sea level.  The  aircraft started sampling  downwind
of the  visible plume and made several passes through  the plume
as it  approached the volcano.  Figure 8  shows two size distribu-
tions  obtained from QCM  data taken on February 28, 1978, (A)
9 miles downwind and  (B)  18 miles downwind.  In these plots,
                                          C = 97.7
              o
                 0.1 -
0.1 ~   1.0     10
  PARTICLE DIAMETER,
                                            100
              (A)  SANTIAGUITO FEBRUARY 28, 1978 - 9 MILES DOWNWIND
                                      C = 425.5
                        0.1     1.0    10     100
                          PARTICLE DIAMETER, jum


             (B)  SANTIAGUITO FEBRUARY 28, 1978 - 18 MILES DOWNWIND


       Figure 8. Aerosol size distribution in the active plume of Volcano Santiaguito,
              February 28, 1978.
                                 144

-------
the mass concentration C^ in stage i of the cascade impactor
was normalized to the total mass concentration C, where C = £ C^.
The Cjyc vs. D plots may be compared with the AC/AlogD vs. D
plots by multiplying C^/C by C/AlogD where C^ is the same as
AC.  These particular plots in Figure 8 show three modes in the
size distribution.  Many of the distributions, however, showed
only two modes.  The plumes were not very uniform and the size
distributions tended to depend on the spatial position through
which the aircraft made its pass.  The particles collected from
the plume were observed with an SEM.  They exhibit the character
of a crystal-rich volcanic magma consisting of crystal fragments
of plagioclase and magnetite.  It is believed that the sub-micron
mode in the size distribution is caused by fragmentation caused
by collisions among the particles.  Since the large particles
are crystalline, they can easily be broken into sub-micron size
fragments by collision.

CONCLUSIONS

     The basic operating principles of a ten-stage quartz crys-
tal microbalance cascade impactor have been described.  It is
designed to obtain real time in-situ data on aerosol size dis-
tribution and to collect aerosols for post-sampling analysis
of their elemental composition and morphology as a function of
size.  Examples of data have been presented which demonstrate
the satisfactory performance of the instrument.  These data were
not obtainable in the past with previously existing sensors.
There are many potential applications of this instrument for
both tropospheric and stratospheric studies and. it is anticipated
that additional atmospheric measurements will continue to be
made using this sensor.

REFERENCES

1.   Chuan, R.L.  Rapid Measurement of Particulate Size Distri-
     bution in the Atmosphere.  In: Fine Particles, Aerosol Gene-
     ration, Measurement, Sampling, and Analysis.  Benjamin Y.H.
     Liu, ed.  Academic Press, New York, 1976.

2.   Woods, D.C.  Measurement of Particulate Aerosol Mass Concen-
     tration Using a Piezoelectric Crystal Microbalance.  In:
     Aerosol Measurements, D.A. Lundgren, et al., eds.  University
     Presses of Florida, 1979.

3.   Woods, D.C.  Rocket Effluent Size Distributions Made With
     a Cascade Quartz Crystal Microbalance.  In: Proceedings,
     4th Joint Conference on Sensing Environmental Pollutants,
     1977.

4.   Rose, W.I., Jr., R.L. Chuan, R.D. Cadle, and D.C. Woods.
     Small Particles in Volcanic Eruption Clouds.  Am. J. Sci.,
     in press.
                               145

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                             PAPER  9
         EXTENDING PRECISION  IN A COMPUTER-BASED  CASCADE
                  IMPACTOR DATA REDUCTION SYSTEM
                          JEAN W.  JOHNSON
                            B.E.  PYLE
                         WALLACE B. SMITH
                    SOUTHERN RESEARCH INSTITUTE
ABSTRACT
     Due to the increased interest in the health effects of
particulates up to 15.0 ym diameter, it has become necessary
to accurately extrapolate the cumulative mass concentration be-
yond the effective limit of the first stage D50  (approximately
10.0 ym) of a cascade impactor.  A first order osculating poly-
nomial is proposed in conjunction with the Computer Impactor
Data Reduction System (CIDRS, EPA 600/7-78-042)  for fitting the
cumulative mass curve between the first stage Dso and the maximum
particle size.  The function is a third degree polynomial which
uses the known characteristics of the cumulative mass curve for
its solution over this range of particle sizes.  Testing this
technique on a number of theoretical unimodal and bimodal size
distributions demonstrates a high degree of accuracy in recover-
ing the true, cumulative, particle concentration <15.0 ym.  The
technique described is proposed for recovering inhalable par-
ticulate from existing data and until such time  that a cascade
impactor is designed with a stage cut of 15.0 ym or greater.

BACKGROUND:  THE COMPUTER-BASED IMPACTOR DATA REDUCTION SYSTEM

     In March of 1978, the EPA report entitled "A Computer-Based
Impactor Data Reduction System" was released,1   The report de-
scribes a series of five computer programs, known by the acronym
CIDRS, which are designed to reduce the field data taken by com-
mercially available round jet cascade impactors.  An outline
of the CIDRS programs is illustrated in Table 1  with a listing
of the program names and their functions.
                               146

-------
               TABLE 1.  CIDRS PROGRAMS AND OUTPUT
                                    MPROG
                    Cumulative mass concentration
-------
particle  sizes.  Both  tabular  and  graphical  outputs  are  produced
at  each of  the data  reduction  levels  described.

      The  curve fit to  the  cumulative  mass  distribution  is  a criti-
cal point in  this data reduction system.   After  the  fit  is made
in  program  SPLINl, the stage by stage values of  cumulative mass,
the D50's,  the stage by stage  values  of  AM/AlogD,  and  the  geo-
metric mean diameters  are  ignored.  Averaging and  penetration-
efficiency  calculations are based  strictly on the  fitting  coef-
ficients  as stored by  SPLINl execution.

      The  method  of fitting used in SPLINl  is a graphical tech-
nique, or a "programmed French curve".   The  Iog10  (cumulative
mass  concentration)  vs.  Iog10  (D50) points are input to  SPLINl
as  illustrated in Figure la.   Then a  parabola is fitted  to each
set of three  consecutive cumulative mass points.  As shown in
Figures Ib  through Id,  interpolated points are defined  at  equal
log diameter  intervals between the first two of  each set of
three D5p's.   (A parabola  having a negative  first  derivative
in  this interpolation  area is  overridden by  a straight  line
between the two  D50's  to ensure a  continuously increasing  cumu-
lative mass curve.)  The final interpolation parabola  (Figure
le) is fitted through  the  second D50,  first  D50l and maximum
particle  size DMAX.

      In the original version of SPLINl,  a  hyperbolic function
of  the form
                     M =  ai  +

is used to define the interpolation points between the first
Dso and DMAX, where M is the mass concentration  (mg/acm) less
than particle diameter D(ym) and aj and a2 are constants.  Seven
equally log-spaced interpolated points are defined over this
broad particle range.  The hyperbolic function as used for point
interpolation is illustrated in Figure If.

     The function which is proposed to replace the hyperbola,
a third-degree polynomial of first order osculation, is the sub-
ject of the remainder of this paper.  Such a function, used to
interpolate points between the first stage D50 and the maximum
particle diameter, is illustrated in Figure 2.  Note that as
the osculating polynomial approaches the total mass loading,
its first derivative goes to zero.  For log-diameters greater
than this zero slope point  (ZSPT) the cumulative mass loading
is at its total value.  The  functional form of the osculating
polynomial is discussed below.  Its importance lies in the fact
that it is a better suited function than the hyperbola for re-
covering the inhalable particulate concentration, . i.e. , the
cumulative mass concentration < 15.0 urn, which lies in this
fitting region beyond the first stage D50  K10.0 jam) .
                               148

-------
5
CO
CO
<
2
Ui
D
O

D50(6) D50i5) D50{4)   D50(3)  D50(2)   D50<1)

                     PARTICLE DIAMETER
 Figure la.  Cumulative size distribution from raw impactor data.
Z
Q
CO

1
UJ
5
o
                                                                      DMAX
      FIRST INTERPOLATION
      PARABOLA
                 INTERPOLATED POINTS
                        i i 11
                                        I'M ""
          D50(6) D50(5) D50(4)   D50(3)  D5Q(2)  D50(1)                    DMAX

                               PARTICLE DIAMETER                       S4181-7

  Figure 1b. Start of development of interpolated points between first and last
                                       149

-------
o
5
<
o
LU
>
D

O
SECOND
INTERPOLATION
PARABOLA
                        INTERPOLATED POINTS
                4-
                   I i i i i i
                                 I'M
          D50(6) D50(5) D50(4)  D5Q(3)  D50(2)  D50(1)                    DM AX

                              PARTICLE DIAMETER
              Figure 1c. Continued generation of interpolated points
z
Q
LU
D

O
         INTERPOLATED POINTS
                      O
                                           THIRD INTERPOLATION PARABOLA
          II  I   I  I I  I I I       I    I   I  I  I  I I  11
            I    I       I       I       I       I
                                                                   i  i  i  i i i
          D50<6) D50(5) D50(4)  D50<3)   D50<2>  D50<1)
                              PARTICLE DIAMETER

               Figure Id.  Continued generation of interpolated points
                                                               DMAX

                                                                  S4181-8
                                    150

-------
5
CO
co
LU
O
                               INTERPOLATED POINTS ON
                               FINAL PARABOLA
                                                       FINAL INTERPOLATION
                                                       PARABOLA
                         00'
          '  ,  '   I  ' ".'
1  I    I I I 1
                                                                    i    i I J
o
z
a
<
o
CO
co
O
          D50(6) D50(5) D50(4)  D50(3)  D50(2)  D50(1)                    DMAX

                              PARTICLE DIAMETER
              Figure 1e. Generation of interpolated points on parabola
                       which includes DMAX.
                                                                 SLOPE = O
             HYPERBOLA AND
             HYPERBOLIC
             INTERPOLATION POINTS
             BETWEEN
             D50 (1) and DMAX
         j	i
                                             •H
                D50(5) D50(4)  D50(3)  D50(2)   D50(1)
                              PARTICLE DIAMETER
                                                                         i i
                          DMAX
                                                                       S4181-9
          Figure If. Generation of interpolated points on  hyperbola through
                    D50(1) and DMAX
                                   151

-------
     The  set  of interpolated  and  original D50 points  is then
used in fitting a series of continuous, second-degree polynomi-
als.  The  fitting coefficients  along with their  boundary points
(the set  of cumulative mass concentration vs. particle size used
in making  the fit)  are stored in  files.  Using these  coeffici-
ents, the  cumulative mass curve and the mass and number size
distribution  curves may be recovered for use in  any subsequent
program.

EXTENDING  PRECISION IN THE MASS SIZE DISTRIBUTION BEYOND THE
FIRST STAGE D50

     There is an increasing interest in the health effects of
particulate matter consisting of  particles up  to 15.0 urn in diam-
eter.  The EPA has begun a large  program to measure the emissions
of this inhalable particulate from stationary  sources.  Also,
efforts will  be made to recover the inhalable  particulate  (IP)
concentration from existing data  by extrapolating the cumulative
mass concentration curve beyond the first stage  Dso limit  to
15.0 ym.
    2
    5
    1
    5
    u
INTERPOLATION
POINTS ON AN
OSCULATING
POLYNOMIAL
            INTERPOLATION
            POINTS ON LINE
            (SLOPE=0) AT
            TOTAL MASS
            LOADING
                                                   il
            t>50<6> D50(5) D50<4)  D50(3)  D50I2)  D50(1)

                            PARTICLE DIAMETER
                  DMAX
                    S4181-10
           Figure 2. Generation of interpolated points on osculating polynomial and
                  zero slope line at total mass concentration.
                                 152

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     CIDRS has proven to be an accurate and time  saving  tool
for impactor data reduction for the size region of approximately
0.25 pm up to 10.0 ym or the first stage D50.2  Because  of  the
present construction of cascade impactors, there  is  a  large span
of particle sizes from the first stage cut point  up  to the  largest
particle size in the distribution.  Due to the lack  of informa-
tion, it is difficult to describe the size distribution  in  this
range of particle sizes.  Since an extrapolation  to  15.0 ym ex-
tends the data only slightly beyond the first stage  D5„, extrac-
tion of IP mass concentration appears feasible if proper extra-
polation techniques are used.

     In view of this an extrapolation method that uses only the
known parameters would seem ideal.  The known or  obtainable
properties of the distribution are:

     1.  The first (largest)  D5o is known.

     2.  The cumulative mass at the first D5o is  known.

     3.  The slope of the cumulative mass curve at this  Dso can
         be calculated.

     4.  The largest particle diameter is known or can be esti-
         mated .

     5.  The total cumulative mass at the largest particle diam-
         eter is known.

     6.  The slope of the cumulative mass curve at the largest
         particle diameter is known (=0.0).

     7.  The slope of the cumulative mass distribution is non-
         negative .

     Until now the function used in CIDRS for fitting  data beyond
the first stage D50 has been a hyperbola of the form given  in
Equation 1.

     Properties 1,  2, 4, and 5 are automatically  satisfied by
this two point fit  (Equation 1).  In addition, the form  of the
hyperbolic function generates a close approximation  to properties
6 and 7 in that the slope of this function for real  data is never
negative and approaches zero at large D.

     However,  the hyperbolic function has drawbacks  which limit
its usefulness for  extrapolation to inhalable particle sizes
above the first stage Dso.  First, property 6 is  never rigorously
satisfied.   While the slope of the hyperbolic function approaches
zero for large values of the maximum particle size,  it will not
be zero for a finite maximum particle size as is  required.  More
seriously,  there is no correlation between the slope of  the hyper-
bola at the first stage D50 and the slope determined by  the spline
                               153

-------
fitting routine.  This discontinuity  in  slope  violates  property
3 of the  true cumulative mass distribution  and thus  the hyper-
bolic function will not define proper mass  concentrations  for
diameters slightly above the first  stage Dso.

THE OSCULATING POLYNOMIAL

     The new technique employs a polynomial of  first order  oscula-
tion to fit cumulative mass concentration from  the first stage
D50 to the maximum particle size.   It not only  passes through
the two end points, but also may be constructed to have zero
slope at the maximum particle size  and have a  slope  at  the  first
stage D50 equal to that of the spline fit through the first stage
D50.  The osculating polynomial may also be constrained to  have
a non-negative slope over the specified  range  of particle sizes.
In other words, all seven of the known or obtainable properties
of the mass distribution in this particle range (as  listed  in
the preceding section) can be satisfied  by  the  proposed technique,

     A polynomial of first order osculation is  used  as  an approxi-
mation to a given function.  By definition  it  matches both  the
function and its first derivatives  at a  finite  number of points.3
In general, there exists a unique  (2n-l) degree polynomial  fit
to a set of n points.  For the case of impactor data, let par-
ticle diameter be represented by the variable  D, the cumulative
mass loading by M(D) , and the osculating polynomial  approximation
of this function by P(D); then properties 1-6  require

          P(Di) = M(Di), and P'(Di) = M'(Di)                   (2)

for i = 0,1 where the first point corresponds  to the first  stage
D50 and the second to the maximum particle  diameter.  For the
approximating equation to be physically  realistic it is also
necessary that property 7 be satisfied;  therefore

               P'(D)  _> 0 for D0 <_ D _< D:.                      (3)

     To first order osculation, the polynomial  P(D)  can be  de-
scribed by Hermite's formula,

                  n                 n
          P(D) =  £  U. (D)M(D.) +  £  V. (D)M'(D.)              (4)
                 i=0  L      x    i=0  1       1

where M(Di) and M1 (Di) are the known values of  mass  concentra-
tion and its derivatives at D0 and  D^- thus n  has values of 0
and 1 only.  The functions Ui(D) and Vj.(D)  can  be expressed in
terms of the Lagrange multipliers Li(D)  and their derivatives
Li1 (D)  such that

                       "                         2             (5)


                                                               (6)
U^D) =j"l-2Li'(Di)  (D-D^lfL
                154

-------
where

                              n   (D-D.)
                                                               (7)

                     i =  0,1,2 , ---- ,n.

For the two points  i = 0,  i  =  1  we  have from Equation 7

                                  _
                    Ll(D)  =       L-                            ,9)
                             DI  -  DO

and their derivatives  are


                           =                                  U0>
For the points  i =  0,  i  =  1  Equation 4 becomes

P(D) =U0(D)M(D0) +U1(D)M(D1)  +V0(D)M'(D0)  + Vj (D)M' (D! ) .   (12)

Combining Equations  5  and  6  with 8,  9, 10, and 11, the osculat-
ing polynomial  then  becomes
+ I"(D - Dp)  (D - DI) 2 M' (D0)1

  L          (D0 - Dx)2       J

                        ' (Di)1

                             J'
                             - D,)
                                      - D0)
                                                               (13)
Equation 13 can be put  into  a  simpler form by defining the follow-
ing constants:
                                155

-------
          M(D0)
     a2 =

     a3 =




     a,. =
          (D0 - D,)

            2M(D1)
            (D,  - D0)
                     3'
                   2M(D0)
                   ~~"
                   (D0  - D,)3

                   M'(D0)

                   (D0  - D,)
                                      2'
                                               (D, - D0)
                                               (D, - D0)
        = k
[kx  +  k3  -  (2  Dj  + D0)  (k2 + ks)  - (2D0 + D^

[(k2 + ks)  (D? +  2 DoDj)  + (k,, + k6)  (D2 + 2D0

         -  2kiD!  - 2k3D0]

[k^2  + k3D2  - D0D2(k2  + ks)  - D2Dt (k, + k6)]
                                                               k6)]
In terms of these constants, the first order osculating  poly-
nomial can be written as a cubic equation in particle diameter
D such that
                    P(D) =

and its first derivative is
                      + a2D  + a3D +
          P1 (D)  = 3ajD2 + 2a2D + a
                                             3.
                                                              (15)
                                                              (16)
     Property 7 above for impactor data limits  the  acceptable
solutions 15 and 16 to those for which

                    P1 (D) >_ 0, D0 £ D 1 Dx.                   (17)

     For some combinations of impactor data, particularly  those
for which the slope M' (D0) of the cumulative mass distribution
at the first D50 is large, property 7 places an upper  limit  on
the range (D0 to Dx) of permissible particle diameters.  For
those cases, physically acceptable solutions can be found  for
a reduced range of particle diameters wherein  the maximum  size
is somewhat smaller than  the original Dj or assumed maximum  par-
ticle size.  Figure 3 illustrates this.  The first  fitting oscu-
lating polynomial has the proper cumulative mass loading value
at the first D50 and at the maximum particle diameter.  The  first
derivative of the function at these two particle sizes  is  also
correct, i.e., the first  derivative of the osculating  polynomial
with respect to log diameter is the same as that for the spline
fit at the first D50 and  is zero at the maximum particle size.
However, since the osculating polynomial does  have  negative  first
derivative values for D0
-------
tested for negative first derivative values for  Do£D£Di.   The
particle size  DI  continues to be  redefined at smaller values,
and  the osculating polynomial is  fit between Do  and DI  until
DI is  defined  at  a critical value such  that there  are no  negative
derivatives over  the  tested particle size  range  for the oscu-
lating polynomial.  DI,  renamed  "zero slope point", ZSPT,  marks
<
O
CO
CO
D
O
                                                          1ST FIT (THROUGH
                                                          ORIGINAL DMAX)
                                                FINAL (CRITICAL) FIT
                          DO
                         (D50(D)
(ZSPT)
(DMAX)
                               PARTICLE DIAMETER
                                                                   S4181-11
      Figure 3. Fitting the cumulative mass distribution for DQQ(1)<^D0 for DQ
-------
the maximum of the osculating polynomial at the total cumulative
mass loading.  As illustrated in Figure 2, interpolation points
for the cumulative mass distribution are then defined along the
osculating polynomial for D50(1)£D£ZSPT and are defined as the
total cumulative mass loading for" 'ZSPT
-------
error in  IP  recovery may be caused by assuming a largest particle
diameter  (100.0  jim here) which is too small  with respect to the
20.0 vim MMD.

Variation of  the Geometric Standard Deviation of the Particulate
Mass Distribution

     To test  the sensitivity of this fitting technique to dif-
ferent values  of the aerosol geometric  standard deviation, og,
unimodal particle-size distributions having  Og values of 1.5
to 3.5 were  tested.   Figure 5 shows the ratio of recovered to
true inhalable particulate IPR/IPT vs.  these values of o~ for
stages having  collection curves with geometric standard devia-
tions of  1.3  and 1.06.  The technique shows  good accuracy in
recovering the true IP concentration.   The highest ratio value
here is 1.04  for a relatively sharp mass  distribution with stand-
ard deviation  of 1.5.  The accuracy increases as the particle-
size distribution broadens.


Q.
HI
D
OC
t—
i
VERED
O
LU
OC

I.UO
1.05
1.04

1.03
1.02
1.01
0.99
I I I ? " ~ ' "
ASSUMED DMAX = 100.0 Aim
_ og = 2.5
LEGEND
0 crgs = 1-3
• ags = 1.06
— —
_ •
IB
-OB
[H
i . • i








1.0 2.0 5.0 10.0 20.0 100.0

MASS MEDIAN DIAMETER (MMD), Aim S4181 12
         Figure 4. Ratio of recovered to true inhalable particle concentration versus
                mass median diameter of a unimodal log-normal particle size
                distribution
                                159

-------
Variation  of  the Geometric  Standard Deviation  (Slope)  of the
Collection Efficiency Curve

     The geometric standard deviation of the collection effi-
ciency  curve  of the sampler,  Ogs'  ranges from  a  near perfect
cut value  of  1.01 to 1.7  in this test.  As shown in Figure 6,
the variation of OgS has  little effect on an accurate recovery
of the  inhalable particle concentration.  The  maximum error for
IP recovery occurs for a  sampler efficiency ags  of 1.01.  Here
the recovered over true inhalable  particulate  ratio, IPR/IPT,
is only 1.02.

Variation  of  the Assumed  Largest Particle Diameter in the Distri-
bution
     In  this  test the assumed  largest particle  diameter, DMAX,
is varied  from 20.0 ym up  to 999.0 ym for the same unimodal log-
normal size  distribution.   The results, as  seen in Figure 7,
show that  accurate IP recovery is relatively insensitive to as-
sumed DMAX unless it is extremely undervalued.   In this distri-
bution the ratio of recovered  to true inhaiable particulate
IPR/IPT  has  its highest values of 1.07  (for ags = 1.06) and 1.06
(for aqs = 1.3) for an assumed DMAX of  20.0 ym.  However, for
this size  distribution having  a mass median diameter of 5.0 ym,
2=  1.04
in

cc
i-
&

o
LU
CC
LU

O
O
111
CC
       1.03
       1.02
       1.01
       1.00
       0.99
                                            I       I      I
                                          ASSUMED DMAX = 100.0
                                          MMD = 5.0 urn
                                               LEGEND
          O ags
                                                    1.3
                                                    1-06
                 I
I
                                        I
J_
          0.0     0.5     1.0      1.5     2.0     2.5     3.0     3.5     4.0

                      GEOMETRIC STANDARD DEVIATION, ag            S4181 13


     Figure 5. Ratio of recovered to true inhalable particle concentration versus aerosol
            geometric standard deviation of a unimodal log-normal particle size distribution.
                                 160

-------
UJ
0
HI
DC
UJ

o
o
UJ
CC
    1.02
    1.01
    1.00
1 1
A
_ A
1 I
1 1 1
ASSUMED DMAX = 100.0 jum
MMD = 5.0 urn
ag=2.5
A A A
1 1 1
       1.01 1.06               1.3            1.5            1.7

                      STAGE EFFICIENCY STANDARD DEVIATION, ags
                                                                            S4181-14
    Figure 6.  Ratio of recovered to true inhalable particle concentration versus stage
              efficiency standard deviation using a unimodal log-normal particle-size
              distribution.
I.U/
1.06
1.05
o.
"J 1.04
cc
oT
RECOVERED I
b b
rs) w
1.01
1.00
0.99
1C
M III I
MMD = 5.0 nm
ag=2.5
LEGEND ~
0 ags = 1.3
• ags = 1-06 -

: . . ;
a a o
i iii i





,

1.0 20.0 50.0 100.0 200.0 500 1000.0
ASSUMED LARGEST PARTICLE DIAMETER, DMAX, /im S4181-15
  Figure 7.  Ratio of recovered to true inhalable particle concentration versus assumed
            largest particle diameter using a unimodal log-normal particle-size
            distribution.
                                        161

-------
an assumed DMAX of 20.0  ym is unreasonably  low.   The other  I
values  are on the order  of 1.01 to 1.02.  It  is  concluded then
that  only an extremely low guess of DMAX might cause large  errors
in IP recovery.  This data reduction method still produces  good
IP recovery if the assumed DMAX is overapproximated.

TESTING WITH BIMODAL PARTICLE-SIZE DISTRIBUTIONS

      For bimodal testing  a log-normal mass  distribution is  used
having  mass median diameters  of 2.0 ym  (MMDX)  and 15.0 ym (MMD2)
and geometric standard deviations, ag  and  og  ,  of 2.0 for  each
mode  unless otherwise specified in the text.  2As in unimodal
testing the masses are collected using stage  efficiency standard
deviations, ags, of both  1.06 and 1.3 to simulate greased sub-
strates and glass fiber  substrates, respectively.  Also, unless
otherwise specified, the  assumed largest particle diameter, DMAX,
is input as 100.0 ym, and  there is an equal contribution of mass
from  each of the two modes.

Variation of Geometric Standard Deviation of  the Particle-Size
Distribution

      In this test, the geometric standard deviations of each
mode  of the particle-size  distribution, agi and  ag , were varied
from  1.5 to 3.0.  As seen  in  Figure 8, the  recovery of inhalable
                                                                 m
-  1.00
DC
UJ


8  0.95
UJ
oc
   0.90
   0.85
                T
                         ASSUMED DMAX = 100.0 urn
                         MMD-! = 2.0 Mm  MMD2 = 15.0 ^m
                         FRACTIONAL CONTRIBUTION OF MODES: 0.50/0.50
                                    LEGEND

                                   O ags = 1.3

                                   • ags = 1.06
                               I
I
     1.0
                1-5         2.0         2.5         3.0

                 GEOMETRIC STANDARD DEVIATION (ag1 = ag2)
                                                            S4181-16
  Figure 8. Ratio of recovered to true inhalable particle concentration versus aerosol
         geometric standard deviation of a bimodal log-normal particle-size
         distribution.
                             162

-------
particulate appears more  sensitive to  this  change of parameter
than  any other test.  For  a stage efficiency ags of 1.06,  the
recovered IP is as much as 14% low for  a  distinctly bimodal dis-
tribution where geometric  standard deviations ag1 = ag2  =  1.5.
As the  modes broaden, the  recovered to  true inhalable particulate
ratio IPR/!PT approaches  1.0.   This should  be expected since
the degree of curvature decreases in the  cumulative mass distri-
bution  as these modes broaden; i.e., the  distribution becomes
more  unimodal and the spline fitting technique must make less
drastic attempts to adjust to curvature.

Variation of the Mass Median Diameter of  the Second Mode
     As  seen in Figure  9,  variation of  the  mass median diameter
of the second mode, MMD2,  has little effect on the accuracy of
IP recovery.  The recovered  to true inhalable particulate  ratio,
IPR/IP-T,  remains at or  less  than 1.05 as  the MMD2 ranges from
5.0 ym to 30.0 ym.  The  highest value of  IPR/IP? of 1.05 occurs
for an MMD2  of 30.0 ym.  This may be attributed to the large
amount of mass in the second mode which falls beyond the first
       1.05
    LLJ
    D
    DC
    CC
    LLI

    o
    o
    LLJ
    CC
1.00
       0.95
                      I        I     I   1^
       ASSUMED DMAX = 100.0 (tm
       MMD-] = 2.0 jum

       ag1 = ag2 = 2-°
       FRACTIONAL CONTRIBUTION OF MODES: .50/.50


                 LEGEND
                 O ags = 1.3

                 B ogs=1.06
                      I
I
I   I
I
         1.0                 5.0      10.0   15.0 20.0  30.0

                 SECOND MODE MASS MEDIAN DIAMETER, MMD2, Aim
                                                       100.0

                                                     S4181-17
        Figure 9. Ratio of recovered to true inhalable particle concentration versus second
               mode mass median diameter of a bimodal log-normal particle-size
               distribution.
                                163

-------
Variation  in Fraction of  the  Total Mass Contained  in Each of
the Modes

      In  this test the ratio of  mass contributed  by each of the
two modes  in the bimodal  distribution was varied.   Beginning
with  a 25%  contribution of mass in the first mode  and a 75% con-
tribution  of mass in the  second mode, the ratio  was changed on
each  trial  with a greater fraction of mass being contributed
by the first mode in each successive trial.  Figure 10 shows
that  the recovery of inhalable  particulate less  than 15.0 ym
of this  bimodal distribution  is acceptable regardless of the
ratio of modes.  The ratio of recovered to true  inhalable parti-
culate IPR/IPT is at its  lowest value of 0.931 for glass fiber
substrates,  where the ratio of  first mode mass to  second mode
mass  is  0.25/0.75.  As mass becomes less concentrated at sizes
greater  than the first stage  D5o,  i.e., as the mass mode ratio
approaches  0.75/0.25, IPR/IPT approaches a perfect 1.00.
1.00
a.
UJ
cc
a
HI
cc
£ 0.95
O
0
111
cc

0.90
II I I
O
0 •
g ASSUMED DMAX
O MMDT = 2.0 jum
0 ogl = 2.0
I
•

= 100.0 Mm
MMD2= 15.0 Mm
ag2 = 2.0
•
LEGEND
0 ogs = 1.3
• a
• UgS
II I I
0.25 0.35 0.50 0.65
0.75 0.65 0.50 0.35
= 1.06
I
0.75
0.25
       FRACTIONAL CONTRIBUTION OF FIRST MODE,
                              FRACTIONAL CONTRIBUTION OF SECOND MODE, F2
                                                             S4181-18

       Figure 10.  Ratio of recovered to true inhalable particle concentration versus fractional
                contribution of mass from each mode of a bimodal log-normal particle-
                size distribution.
                                164

-------
CONCLUSIONS

     It is concluded from the test results discussed  in this
paper that, for data taken by a round jet cascade  impactor, a
polynomial of first order osculation may be used for  fitting
the cumulative mass concentration curve between the first  stage
D50 and some maximum sampled particle size.  This  function used
in conjunction with the "Computer-Based Cascade Impactor Data
Reduction System"1 provides a method for accurately determining
the inhalable particulate (IP) concentration, i.e., the cumu-
lative mass concentration of particles _<15.0 urn in diameter.
The method does not require the use of a 15.0 pm cut  diameter
sampling device.  It therefore may be used for determining IP
concentration in gas effluents sampled to date by  conventional
impactors.

     To test the accuracy of the osculating polynomial for de-
termining IP concentration, a number of unimodal and  bimodal
log-normal size distributions were theoretically sampled accord-
ing to the impactor's stage efficiency curves and  the resulting
IP concentration was compared to the original values.  Varia-
tions of the mass median diameter and geometric standard devia-
tion of the size distributions, the assumed largest particle
diameter, stage efficiency standard deviation, and fractional
contribution of mass per mode  (in the case of bimodal distri-
butions) were studied as to their effect on recoverable IP con-
centration parameters.

     Good recovery of the IP concentration was obtained for all
"sampling runs", within approximately ± 7%, except in the  case
of sampling a bimodal distribution where the modes are very
sharply defined and with well separated mass median diameters.
Specifically, in sampling a bimodal distribution with mass median
diameters of 2.0 pm and 15.0 urn with aerosol geometric standard
deviations of 1.5 for each mode, the recovered IP concentration
was 14% below the true IP concentration.  The greater degree
of error here is attributed to the sharp changes in curvature
of the cumulative mass concentration curve to which the modified
spline fitting procedure must adjust.   It can reasonably be
assumed that actual field data would fall into size distribution
modes such that the dispersion of each mode could be  described
by a geometric standard deviation value of 1.5 pm or  larger.
Therefore,  the degree of error in recovering IP concentration
using this curve fitting procedure may be expected to be within
the limits of ± 14%.

ACKNOWLEDGEMENTS

     This research was supported by the U.S. Environmental Pro-
tection Agency under Contract No. 68-02-3118, D.Bruce Harris,
Project Officer.  Joseph D.  McCain and Dr.  Ashley D.  Williamson,
at Southern Research Institute, provided information  and helpful
criticism of the paper.
                               165

-------
REFERENCES

1.   Johnson, J.W., G.I. Clinard, L.G. Felix, and J.D. McCain.
     A Computer-Based Cascade Impactor Data Reduction System.
     EPA-600/7-78-042, U.S. Environmental Protection Agency,
     Research Triangle Park, NC, 1978.  592 pp.

2.   McCain, J.D.  A Data Reduction System for Cascade Impactors,
     EPA-600/7-78-132a, U.S. Environmental Protection Agency,
     Research Triangle Park, NC, July 1978.

3.   Scheid, Francis.  Numerical Analysis.  Schaum's Outline
     Series, McGraw Hill, New York, 1968.  p. 65.
                               166

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                             PAPER 10


          IMPLEMENTING  CIDRS  -  A PROGRAMMER'S  PERSPECTIVE
                         CLINTON  E.  TATSCH
                    RESEARCH  TRIANGLE  INSTITUTE

QUALITY ASSURANCE:  THE TOTAL PERSPECTIVE

     As we work with research quality assurance, it is clear
that investigators in various disciplines are becoming aware
that an appropriate quality assurance program is not an add-on
or a separate function that can be neatly applied to existing
programs.  It is increasingly clear that quality assurance can
only be planned and performed in any adequate sense by indivi-
duals who are personally committed to producing high-quality
data.  This commitment is demonstrated by a concern, in the early
planning stages of a project, that estimates of precision and
accuracy be obtained for each measurement or observation.  By
characterizing data quality as the data are collected, it becomes
possible to estimate the quality of the final results.  The most
simple to estimate are relatively straightforward measurements
such as length or weight.  These measurements can be made re-
peatedly and carefully on everyday objects using physically
"comfortable" procedures.  At the other end of the scale, the
assessment of computer software quality, by its very nature,
is difficult to thoroughly check.  The purpose of the computerized
cascade impactor data reduction system  (CIDRS) is to perform
a series of lengthy calculations that cannot be done manually
due to time constraints.  Additionally, as a result of having
this capability of performing more calculations more quickly,
computer programs are becoming much more intricate in their
decision-making (i.e., branching) capabilities;  as this occurs
it becomes more difficult to thoroughly check the validity of
all branching options.  However,  work is in progress along these
lines.  We believe our work with the CIDRS system in the past
few months has been useful in uncovering some of the pitfalls
in the area of software quality assurance.
                               167

-------
     Our objectives in implementing CIDRS are:

         Modify and implement CIDRS coding for the computer in-
         stallation at Research Triangle Institute

         Execute documentation examples

         Begin sensitivity analysis

     •   Make changes in such a way as to be most useful to other
         users

The first three were in the task directive from EPA:  we com-
pleted the first two, and began work on the third objective.
The fourth objective, that of making changes in the fashion that
we did, developed shortly after we began work, and eventually
assumed a place of major importance.

IMPLEMENTATION:  AN OVERVIEW

     In order to make any evaluation of CIDRS, it had to be exe-
cutable on our computer.  CIDRS was developed on a PDF 15/76
over a period of several years; hence the goals and intent of
the system have changed significantly since the early code was
written.  In order to execute CIDRS programs, the source code
must be readable and compatible with the resident FORTRAN com-
piler.  The control language used must also function on the local
computer system.

     With this in mind, we obtained a tape containing CIDRS from
Southern Research Institute and began its implementation on the
IBM 370/168 at the Triangle Universities Computing Center  (TUCC).
CIDRS is made up of six mainline programs as shown in Figure 1.
These programs run independently of each other with the excep-
tion of the generated data files, which are used by various pro-
grams of the system.

     As indicated in Figure 1, MPPROG takes the raw impactor
run data  (flow rate, temperature, gas composition, stage load-
ings, etc.) and generates data file KMC001, which contains cumu-
lative mass distribution data.  For each impactor run, these
data are used in the curve-fitting program SPLIN1 to generate
FILSPL, which contains the fitting coefficients discussed earlier
These two physical files may contain data for up to 50 impactor
runs with the only stipulation being that the same type of  im-
pactor must have been used for each run on the file.  These two
files, KMC001 and FILSPL, then serve input to GRAPH, which pro-
duces plotter output for visual checks on the individual or
combined runs, or as input to STATIS, which then averages the
series as into one set of interpolated points with confidence
limits corresponding to all the runs on the file.  The stipula-
                               168

-------
9«vlc« OUTLET
Raw Data
\
/
                                                 Printer
                                                   Output
                         Fi«n\J   g^j  I/
Figure 1. CIDRS program relationships.
                169

-------
tion embedded in the logic of the system is that all the  impactor
runs included in the KMC001 and FILSPL data files should  be
logically related to process conditions.  This may conclude the
calculations.  However, if a pollution control device is  being
evaluated, the data for the associated inlet and outlet measure-
ment series are processed independently, starting at MPPROG.
One series of data files then relates to data collected at the
inlet of the control device; the other series relates to  data
collected at the outlet of the control device.  After the data
are separately averaged in STATIS, the JWJ001 and JWJ002  files
are used by PENTRA and PENLOG to calculate collection efficiency
(or penetration) for the control device involved.

     As indicated in Figure 1, the first two programs in  the
series, MPPROG and SPLINl, use direct access files and the system
card reader and printer, whereas the last four, GRAPH, STATIS,
PENTRA, and PENLOG, use the system plotter as well as direct
access files and the system printer.  In the case of CIDRS,
plotter usage is proving to be the major source of trouble in
implementing the system.  The protocols for addressing peripheral
equipment from within an executing program vary not only  from
manufacturer to manufacturer, but from installation to installa-
tion, due to the varying local perspectives.

     The basic difficulties one might expect to encounter in
implementing CIDRS would be:

     1.  Differences in the specific version of FORTRAN used
         from one machine to another, and

     2.  Local idiosyncrasies.

CIDRS:  OUR EXPERIENCE

     The basic approach we took to implementing the CIDRS system
was to modify the original source code as little as possible,
using the IBM Utility IEBUPDTE to insert only the necessary
changes for each run.  In this way, we developed a set of six
modification packets, as indicated in Figure 2, which are applied
in a two-step fashion, thus leaving the original source code
intact and consistent with the documentation.  We took this
approach rather than physically modifying the original source
code because in most cases the same types of changes will need
to be made at other installations using, for example, a Univac
or CDC machine, and leaving the modifications intact will high-
light necessary changes for subsequent applications programmers.
We also used the WATFIV interpreter for most of the initial work,
which meant that we executed from source code every time  rather
than going from object modules, thus getting more thorough diag-
nostics .
                               170

-------
       Editing
        File
 "Original"
SoRI Source
  File
                      MASTER
 Edited,
Compilation-ready
  File
                                                 compile,  etc,
         Figure 2. Structure and use of modifications to original CIDRS logic.
     The difficulties  we  encountered in implementing CIDRS on
our computer system were  all  installation-specific problems and
for the most part could be  solved in a very straightforward but
laborious way.  One problem we  encountered was the difference
between IBM and Digital Equipment protocols.  A second, more
frequent problem involved the I/O handlers.

     The hardware-related problem that we identified was that
the PDF 15/76 apparently  clears core after each job, whereas
the IBM 370/168 does not.   This showed up in various places as
uninitialized variables.  Since the IBM FORTRAN-G compiler does
not easily check for uninitialized variables, out-of-bounds array
addresses, etc., the WATFIV file interpreter was essential to
uncovering the uninitialized  variables.  We feel it did a thorough
job.

     At the outset, the FORTRAN I/O Unit numbers were converted
from constants to integer variables as shown in Figure 3.  The
mnemonics RDR, PTR, defined as  four byte variables, were used
and their values supplied in  a  data statement at the beginning
of the program as shown in  Figure 4.  Not only does this enhance
the readability of the source code, it also means that the unit
numbers for the reader and  the  printer may be altered by chang-
ing one or two data statements  rather than by searching through
the entire source listing for places that the reader and printer
are used.  We feel this should  be done generally, not just for
programs written for distribution,  because it never can be antici-
pated when system programmers may decide to change unit numbers
to upgrade or modify the  system.
                               171

-------
to
                        602  DU 650
                            JF(IK£PET)605,6i5,605
                        605  REAlfl2J902)MPLOTtJl_f J21J3,J«/JS,J6

                        615
                        650  CONTINUE

                                         Figure 3a.  Sample I/O statements, as received.
                        U -650- Ls
                       IF (1^0)605,015,605
                 605
                 615™  rtRITE(GRAPMO'L)MPLOT,Jl,J2* J3V J«» J5,J6,JP1
                      X
                   650 COf4TINUC
                                          /S'tyre 36.  Sample I/O statement, as modified.

-------
      INTEGER RDR,PTR>KMC001,FlLSPLrGRAPHO
      DOUBLE PRtCISION  XNDPtN(10),YO(10)
           Figure 4a.  Specification of I/O unit mnemonics 4-byte integer variables.
 C *  »*»  -> «> ASSIGN  1/U UNiT  NUMDEftfry-CTC, HERE
 C *
       DATA RDR/l/,PTR/3/
 •€-*	
•-€-*-
        DATA KMCOO1/1O/	
       -DEFINE-FI L€-i   •>  ->   OON'T  FORGET "FILSPL" DEFINITION IN  SUBROUTINE  FIL3PL
 C
           Figure 4b.  Data definition statements for defined I/O unit variable.

-------
     The only  significant difficulty we encountered had to do
with the interface to the plotter; this raises  an issue that
has been anticipated and for which there appears  to be a general
solution when  program systems of this nature  are  being developed.
The actual working code can be written in  such  a  fashion that
I/O interfaces are localized into one subroutine,  which clearly
makes all installation-specific references  to a particular device
and then, in the  rest of the program, all  the I/O can appear
symbolically.   As an example of this concept, I will describe
how we handled the graphics part of the last  four  programs of
CIDRS, using modifications to GRAPH as an  example.

     As shown  in  Figure 5a, plotter commands  available on Southern's
PDP-15 treat the  plotter as an I/O device  with  a  unit no. 7.
This way it is quite logical to have statements such as those
shown in Figure 5b to either write to a device  or  read from the
device (in the latter case it means reading the location of the
pen).  However, at the TUCC installation such detailed control
of the plotter is not possible; it can only be  accessed through
high-level subroutine calls.  Therefore, we went  through the

          WRITE (7) mode (followed by optional variables, depending on
      the value of mode).
Mode
0
1
2

3

4
5

6
7
8

9
10
Pick up the pen
Put down the pen
Move to absolute coordinates. Address with
pen up
Move to absolute coordinates. Address with
pen down
Move to delta coordinates. Address with
pen up
Move to delta coordinates. Address with
pen down
Draw character (see note below)
Set coordinate address
Move to absolute coordinate address
(no pen change)
Move to delta coordinate address (no pen
change )
Set character attributes
Additional
variables
None
None

IX, IY

IX, IY
IX, IY

IX, IY
ICNT, DATA
IX, IY

IX, IY

IX, IY
IXSI2, IYSIZ,
ISIN, ICOS
                 Figure 5a.  Plotter specifications from Reference 2.

             wRITE(LOTS)
               U™»QNJr^ f Q v * vu %
               » f\ ' i */ (k w A ™ A Q f
             JYsRND(SY*YB)
            _        _
            WRl tE~TLOTS) MQDE7IxTfY

                 Figure 5b.  Sample plotter output statement, as received.

                                174

-------
 source  code  replacing  each  plotter  I/O  statement  with  a call
 to  a  newly written  interface  subroutine.   This  type  of call
 should  be valid,  independent  of  any hardware, and the  result
 is  that the  program logic now accesses  a  subroutine, passing
 along values through arguments and  through common which will
 be  of use for  the plotter.  The  plotter interface then is  written
 as  being hardware-dependent.   In this way all the necessary data
 are available  to  the interface subroutine,  both physically and
 logically, and all  changes  relating to  the plotter are physically
 isolated to  the subroutine.   Again,  our basic approach was to
 design  the interface subroutine  PLOTTR  to mimic the  originally
 used  read and  write statements.   This approach  would probably
 be  simplified  if  the I/O interface  had  been written  at the outset
 as  these programs were being  developed.   To keep  things as con-
 sistent as possible with the  original CIDRS programs and documen-
 tation, we elected  to  mimic the  behavior  of the PDP-15 plotter
 at  least in  the original code.   In  Figure 6, it may  be seen how
 we  accomplish  this;  at the  left  is  the  old write  statement,  which
 would move the pen  to  specified  coordinates; to the  right  is
 the equivalent subroutine PLOTTR call.  It may  be noticed  that  the
 first parameter in  the argument  list is the "mode" of  the  corre-
 sponding write statement.   Thus,  Figure 7 shows that when  PLOTTR
 is  entered the first thing  that  is  checked (following  some initial
 housekeeping)  is this  mode  value, which then determines what
 is  to be done  by the plotter.  Once the branch  is taken, the sec-
 tion  of code which  directly relates to hardware requirements is
 entered.  These blocks, as  illustrated  in  Figure  8, will need to
 be  modified  for application at other installations.  These  blocks
 are very installation-specific and one would expect that an
 applications programmer would  go  to this  section  of the  program
 and make the necessary changes.   Given the  presumption  used  in
 making  this  kind of  interface, and  knowing  the  requirements  of
 his own system  then, one would expect the programmer would  be
 capable of quickly  and reliably making the  changes necessary to
 implement each particular program on his own system.   Using  this
 approach we  have exercised all six CIDRS programs and all  function
 reliably as  far as  we  are able to tell.   We have  not been  able to
 extensively  test the programs, but, to the  best of our  knowledge,
 the programs do function as they were intended.


 GENERAL REMARKS

      A  data  validation section would be useful  in CIDRS as  a
 quality assurance check, and  it  appears this easily could  be
 added.  For  example, in MPPROG it would be  appropriate  to  de-
 termine the  type of  "window" that is reasonable for each input
parameter;  this could  be done  a priori,  as  well as from  the  tech-
nical experience of  the programmer.  For  instance, one  would
not anticipate that a negative weight would be  a  valid  entry.
Although a weight change less  than zero may be physically ob-
served,  a negative weight would not be feasible nor would  a
                               175

-------
-J
cr>
       c
       c
              ENTRY
 IYcRND(RINC*H)
 IF(IX.LE.O) IX«10
TFTiY.LE.O)_IY«10
"JSINS65536*
"JCOSa6553b*
 MODY3TO
 wRJTEUOTS) MODE*IX,|Y,JSJN,JCOS
 IX 5 R NP(SX«XB)      	
TT=R"ND(SY*YBl        ~~	~— ~~
                                         C SETS CHARACTER/PLOTTED  ATTRIBUTES,- RAISE
                                         C	& MOVES-TO  STARTING -POSITION—-

                                         C-                                       SEf
                                               IX=RND(RINC*W)
                                                            IF(IX.LE.O) IX»10
                                                            IF(IY.LE.O) IY»10
                             (COS(TH)f
JCUS=6553<>*
MODE=10
                                                               (COS(TH))
             ;WRITE (LOTS) MODE", 1X71Y  *irsf--mm — ~* ^»CALL PLOTTRC2,XB,YBi0,,0,)
                                                            RETURN
 ENTRY
 MODEs 2
J_X Qs R NO ( SX * X )
 I Y 0 s H NO 1 3 Y"*YJ
                                                            ENTRY CDGRID (I,X,Y»UrM)
                                                            MODE=2
                                                            IXO«RND(SX*X)
             MUDEsl
 WRITE(LOTS) MODE
 MUDE = 9	_"   ~
JMO\)E 8 s8 '"	"""
 LlMifsM'+l
 IF (I,EQC2*
_MY2sO	
 MY1=0
 MX 1*5  	"
                                               CALL PLOTTR t2VX>T/0.10.)
                                               MODE=1
                                                            MOD£s9
                                                            MODE8s8.
                                GO TO 100
                                               IF (I.EQ.a*(I/2))
             GO  TO  ISO
         
-------

IFCMODE.EQ.14)GU TU 14
' X=XX • 	 	 " ' 	 " 	 ' "
Y-YY
HSHM
TSTT
DX=HH
OT-I 1
- XS=X*XSCL ~" 	 " """ 	 "" 	 	
YS=Y*YSCL
DYScDY*YSCL
IF(ICNT,EQ.UlNRITE<3,i002)ICUT
1002 FORMAT (• »>rflS,'|*r
-------
oo
 C  THIS BLOCK SERVES CALLS FOR                                CMODE«0)      00056082
 C  ,  .  . PICK UP THE PEN                                                    00056083
 tfrrO— • -t(MT IttUE -- - — - — -- - - - - - - - - 88-7
 C  --  . --------- •-*.»*-»--»••»»»•.....».»  00056088
 C  THIS BLOCK SERVES CALLS FOR                                (MODE*l)      00056089
 C  ',  .  , PUf-PEtt-frQwtt— - - — ~ — ~ -- — - — - - - - — — — t>tf05t»0*0
 I--- - CONTINUE     -   -  —• ------------------         ------ ......  - ....... -------  --- ..... — ..... —00056091
              PNDM— '   ------------------------- ----------------------------------------- 00056092
              OnX3f-Y8yt1»NWO-- — — --- ----- ' — -— — -- r— -- - — .,_™_^OT) 5^4,3
       RETURN                                                               ©0056094
                                     -«.--. ...»«i»^ ••«.»»,  00056Q«?5
                                     _—-_____—_----
 €-.--.—. -MOVE- TO- ex, t )> -WITH-PEW-UP
 -2 ----- CONTINUE --------
 - -- PC-mjP*tP WP— - - -- -—,_ - -._-,
       CALL PLOT(XS,YS»IPNUP)                                               00056100
       RETURN                                                               00056!0t
 -€»^^CT3-.., -jr» ••JTJ1 «B.»»lg.aam^» ^r^r^-^-^ -."»"m'^ » ,-^-^-^-tHH>5M w
 C- THIS BLOCK SERVES CALLS FOR --- ...... — ..... —  ---------------- ~~
-------
weight increase of, for example, greater than 50 mg be reason-
able.  So, for the stage weights, a data validation section might
include a check that the weight is not negative and the change
is not larger than 50 mg.  In terms of data quality and of being
more assured of the functioning of the programs, this type of
approach to screening both the input data and the control param-
eters is being looked into and may become part of a subsequent
version.

     Another aspect of data quality that is of concern is the
fact that these programs will be modified to run on different
operating systems.  Also, depending on the user's perspective
and needs, he may decide that he wants to modify some of the
basic algorithms to alter the output.  In this situation the
program system no longer is CIDRS, but is a local modification
of CIDRS and in any documentation it should be made clear just
what these modifications are.  Otherwise, comparing data between
two operating groups will be questionable or impossible simply
because a different physical meaning due to the different mathe-
matics involved may very well have occurred.

     In summary, we have obtained CIDRS as distributed by Sou-
thern Research Institute.  We have implemented it in an environ-
ment different from that in which it was developed, attempting
to locate and highlight identifiable problems and to design modi-
fications that will be useful to other users installing CIDRS
on their system.  CIDRS appears to be a very useful and well-
written set of programs, especially considering that it is the
first generation package.
                               179

-------
                             PAPER 11
         NUMERICAL  SIMULATION  STUDIES  AND  DATA  REDUCTION
            FOR  SIZE CLASSIFYING MEASUREMENT  TECHNIQUES
                            H.  FISSAN
                            C. HELSPER
                        AEROSOLMESSTECHNIK
                    GESAMTHOCHSCHULE DUISBURG
ABSTRACT
     Nearly all techniques that classify particles to obtain
size distributions show a certain cross-sensitivity.  Only a
certain fraction of the particles belonging to one class of par-
ticle size is represented in that class while the rest is found
in the neighboring classes.

     Since generation techniques for monodisperse aerosols have
been developed, it is possible to describe this non-ideal instru-
ment behavior by rather straightforward calibration experiments.
The knowledge of this systematic error makes it possible to
simulate the instruments numerically for given size distribu-
tions.

     The influence of the non-ideal instrument behavior on the
measured distribution parameters is discussed for a wide range
of possible distributions.

     A data reduction program has been tested by simulation
studies for various unimodal and bimodal log-normal distribu-
tions.  The influence of random errors in the measured data on
the results of the correction calculations is discussed.  Finally
the data reduction program has been applied to several real
aerosols.

INTRODUCTION

     For several reasons there is an increasing interest for
the determination of the size distribution of aerosols.  For
this purpose various measurement techniques have been developed
which allow classifying the particles according to their size-
dependent behavior into a number of size intervals and deter-
mining a measure for the particle frequency in these intervals.
The size of a particle is normally represented as the equivalent


                               180

-------
diameter of a sphere which would show the same  reaction  as  the
measured particle.  So this equivalent diameter depends  very
much on the measurement principle used.  The particle  frequency
is mostly determined as particle number or particle mass or as
a number or mass concentration.

       For all these measurement techniques the classification
procedure as well as the determination of the particle concen-
tration is not free from certain systematic errors which may
cause considerable differences between the real size distribution
and the one determined by the instrument.  If this non-ideal
instrument response is known, one can estimate  the influence
of these effects and can try to correct the measured data to
obtain a size distribution nearer to the real one.

REAL INSTRUMENT RESPONSE OF SOME CLASSIFYING MEASUREMENT TECH-
NIQUES

     This non-ideal instrument behavior, though predicted by
theory in most cases, has often been neglected  in the past, be-
cause there was nearly no possibility to describe these  effects
exactly.  Since monodisperse aerosol standards  like the  vibrating
orifice generator or the electrostatic classifier are available,
this situation has changed and a lot of work has been done on
the calibration of classifying instruments.

     So the electrical aerosol analyzer (EAA) has been calibrated
by Liu et al.1 and its response to monodisperse aerosols has
been represented by a calibration matrix.  The cross channel
interference shown by this matrix is mostly due to the mere
statistical distribution of the number of elementary charges
on particles of the same size.

     An optical particle counter (type Gertsch HC-15) has been
calibrated by OOP particles in our lab.  This instrument has
a very small scattering volume which allows measurement of par-
ticle concentrations up to 105cm~3 with still neglectable coin-
cidence errors.  As the cross section of this scattering volume
is smaller than the cross section of the sample stream, a certain
number of particles cross the edge of the volume, thus scattering
less light than a particle in the center of this volume.  This
is the reason for a considerable cross channel interference of
this device.   Figure Ib shows the instrument response for several
monodisperse aerosols as a cumulative number distribution versus
the particle diameter indicated by the instrument.

     The fraction of particles measured too small increases with
increasing particle size because of the increased probability
for those particles to pass partially outside the scattering
volume.   Calibration studies in the lower particle size range
are now done by means of an electrostatic classifier.  For com-
parison the equivalent results for a Royco 225 particle counter
                               181

-------
        z
        o
           1.01
        S3 0.8
        cc
        t-

        Q

        cc 0.6
        LU
        m

        D

        ui 0.4
        = 0.2-


        O
               ROYCC 225/241
                                                                 10
                                PARTICLE DIAMETER Dp,
           1.0
        m 0.8-1

        E
        i-
        cc
        U
        00
          0.6-
        z 0.4 H

        LU
          0.2-
        O
                HC IS
               B)
23           5

  PARTICLE DIAMETER.Dp, /urn
                                                                 10
                 Figure 1. Calibration results of optical particle counters.
are  shown  in Figure  la.   The scattering  volume  of this  instrument

is limited  by the  sample  stream  so that  all particles pass it
with the whole cross-section.  Therefore the instrument behavior
is nearly  ideal.
                                   182

-------
        Similar calibration  experiments have been  done for a six-
stage  Andersen Stack Sampler  (A.S.S.)2 with liquid  oleic acid
particles  to determine the  collection efficiencies  of the stage
as well as the wall losses.   In Figure 2 the percentage of total
wall loss  is plotted against  the aerodynamic particle diameter.
Results of Gushing et al.3  for  an eight stage A.S.S.  and solid
particles  are given for comparison.   Besides the  fact that the
number of  stages was different  in the two experiments,  the dif-
ferences between the two curves might be caused by  the following
reasons:

     1.    flow, particle density, and temperature were not the
           same in the two experiments,

     2.    the adhesion of solid and liquid particles  on walls
           might be different,

     3.    in Gushing's experiments the impactor was mounted hori-
           zontally, while in  ours it was mounted  vertically.
CO
O
80



70



60



50



40



30


20



10


 0
  IMP ACTOR

V  A.S.S. 6

D  A.S.S. 8
                      PARTICLES  FLOW RATE
                      LIQUID

                      SOLID
22.6 l/min (20°C, 1 BAR)

14.2 l/min (22°C, 1 BAR)
                   23         5            10      15

                      AERODYNAMIC PARTICLE DIAMETER, DAE, jum
                                                        20
          Figure 2.  Total wall losses of Andersen Stack Sampler (Gushing, et al.3).
                                 183

-------
     The collection efficiencies determined in the two experiments
are compared in Figure 3.  Due to bounce off and blow off the
collection efficiencies for solid particles in no case reach
a value of 100%.  For liquid particles this extreme shape of
the collection efficiency curve is only found for the first
stage, where the wall losses cause this instrument response.

INFLUENCE OF NON-IDEAL INSTRUMENT RESPONSE ON THE DETERMINATION
OF SIZE DISTRIBUTIONS

     If one has determined the instrument's response for a set
of monodisperse aerosols, it is possible to establish a response
matrix to describe the instrument's overall behavior.  This makes
it possible to simulate the instrument numerically and to predict
its response to any given size distribution for an aerosol similar
to the one used in the calibration procedure.  The comparison
of the instrument's output with the input distribution allows
estimation of the errors caused by its non-ideal behavior.

     Results of a simulation of the EAA for two log-normal dis-
tributions are shown in Figure 4.  The cumulative number distri-
bution is plotted against the particle diameter.  The geometric
standard deviation for both input distributions which are repre-
sented by the solid lines is Og = 2.0; the number mean diam-
eters are 0.03 ym and 0.3 ym, respectively.  In both cases the
EAA tends to shift the mean diameter of the output distributions
(given by the circles and dashed lines) to smaller values while
the shape of the distribution is not very much affected.  The
influence on the number mean diameter  (NMD) seems to be dependent
on the input NMD.

     This dependency is shown in more detail in Figure 5.  The
ratio of the NMD calculated from the simulated output data to
the actual input NMD is plotted as a function of the input NMD
for three geometric standard deviations Og.  For an ideal in-
strument this ratio should be one, at least for distributions
in the middle of the covered size range, while near the upper
and lower limit of this range, there are deviations due to the
fact that the instrument covers only a part of the distribution.
But the real instrument shows output NMD's which are by 20% too
small even in the middle of its range.  For NMD's smaller than
0.1 ym there are points where the effects of limited size range
and non-ideal behavior compensate.  Around these points the in-
strument will determine a correct output NMD.

     If one calculates under the assumption of spherical par-
ticles a volume distribution out of the measured number distri-
bution there will be deviations between the actual input volume
mean diameter (VMD) and the calculated output VMD, too.  Figure
6 shows the ratio of calculated to actual VMD, plotted against
the input NMD.  The deviations in this case are even more ob-
vious, especially for large standard deviations, which is mainly
                               184

-------
                                    COLLECTION EFFICIENCY,

                                               §
                                                   §
00
U1
              ;n
              I

               .
              §
              3!
              fV

              S'
O
-*>
^


I
1
              I
            p
            (JI
                       3D
                       o
                       D
         I  a
                       m
                       a>

                       D
                              oo
                              O
                               CO
COLLECTION EFFICIENCY,

             s
                                                                                                                               §
                                                              30
                                                              O
                                                              0
                                                                            30
                                                                            H

                                                                            O
                                                                            g
                                                                            >
                                                              m
                                                              30

-------
                 98
                  0.01
    0.1           1.0

PARTICLE DIAMETER, jum
        Figure 4. Calculated electrical aerosol analyzer response for given log-normal
               size distribution.
due to the  limited size range.   As  the EAA sensitivity  to number
concentration depends strongly on particle size, the  number con-
centration  determined with this  instrument is also affected by
its cross-channel interference.  Figure 7 shows the ratio of
the total calculated output number  concentration to the actual
input concentration.  For distributions in the middle of its
size range  the instrument tends  to  give a number concentration
reading which is about 10% too high,  while near the limits of
the size range too small readings are caused by the fact that
only a fraction of the particles is counted.
                                186

-------
Ill
o
  o
              0.01
                                                                             1.0
                                   NUMBER MEAN DIAMETER NMD, j
                Figure 5. Ratio of calculated and actual number mean diameters for an
                         electrical aerosol analyzer.
  Q
  5
  D
  _l

  O
O
                0.01
                                    NUMBER MEAN DIAMETER NMD, jum

               Figure 6.  Ratio of calculated and actual volume mean diameters for an
                        electrical aerosol analyzer.
                                           187

-------
                                                                 = 1.4
S\s
Z
O
P
O
LLJ
CO

D
Z
ui
U
   Ui
u
oc
LU
m
  D
            0.01
                                                             1.0
                         NUMBER MEAN DIAMETER NMD, Mm


         Figure 7.  Ratio of calculated and actual number concentration for an electrical
                aerosol analyzer.
        Similar calculations  have  been done for a six-stage A.S.S.
 Figure 8 shows the results for  three log-normal distributions
 (<7g = 3, MMD = 1.5 and  10 pm) as  a cumulative mass distribution
 plot.  For these calculations the collection efficiencies for
 liquid particles have been used.   One can see that the deviation
 between the input distributions (solid lines) and the simulated
 measured data is nearly neglectable for distributions with small
 mass median diameter  (MMD).   It tends to increase with increasing
 MMD, mainly due to increasing wall losses.

      These wall losses  have  been  simulated for solid and liquid
 particles for a set of  input distributions.  Figure 9 shows  these
 wall losses as a function of MMD  and ag.  In both cases the  wall
 losses reach values of  more  than  30% of the total mass for large
 MMD's.  For solid particles  they  do not very much depend on  the
 geometric standard deviation of the input distribution.

      The ratio of calculated output MMD to actual input MMD  as
 a function of the input distribution parameters for liquid par-
 ticles is shown in Figure 10.   As the impactor does not have
 a lower size limit because of  its backup filter, its behavior
 is nearly ideal for small MMD's.   For larger MMD's and large
 erg's the output MMD is  much  smaller than the one for the input
 distribution.  Besides  the effect of the upper size limit, the
 increasing wall losses  are the  reason for this behavior.
                                 188

-------
                                                                 CUMULATIVE MASS  DISTRIBUTION,  %
         m
         30
         O
         O
                                    P
                                    ui
oo
VD
                                    -
I
cf
                                    Ol


                                >

                                m   -»
                                H   o
                                m
                                30
                       Q.
                       Co'
                       5?
                       Cr
                       C
                       ***•


                       8'
             s
                                                    en

                                            I   I  I  I
                                                                     Is)
                                                                     O
                                                                 S    g

                                                                 1—r
                                   CO
                                   vt
              to
              CO
                                   I  I   I   I
                                                                                                                                     to
                         I   I  I
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-------
     30
     20
     10
 ta
 01
_J
_]


s
     30
     20
     10
             COLLECTION  EFFICIENCY FOR LIQUID PARTICLES


             (V=22.6 l/min)
             COLLECTION EFFICIENCY FOR SOLID PARTICLES


             (V=14.2 l/min)
                     
-------
     0.7-
     0.6 -
                                                               10
                         MASS MEDIAN DIAMETER MMD.
     Figure 10.  Ratio of calculated and actual mass median diameters for A.S.S. (collection
              efficiencies for liquid particles; V = 22.6 l/min).
DATA REDUCTION  TAKING INTO ACCOUNT NON-IDEAL  INSTRUMENT BEHAVIOR

     These  instrument simulation studies show that there are
cases in which  the  errors caused by the instrument response can-
not be neglected.

     A data  reduction procedure which would allow correction
of the measured data should fulfill the following requirements:

     1.   It should allow correction for the  instrument's sys-
          tematic  error even if the response  matrix of the in-
          strument  is highly unstable  (small  errors in the mea-
          sured data will give large changes  in the solution).

     2.   It should reduce the effect of random errors in the
          measured  data by use of physical  constraints.

     3.   It should reduce the amount of data necessary to de-
          scribe the particle size distribution.

     4.   It should allow a certain extrapolation of the results
          over  the  size range covered by the  instrument.  This
          would allow a comparison of different measurement tech-
          niques with only small overlapping  size ranges.
                                191

-------
     To obtain these requirements, it seems to be reasonable
to make the assumption of a certain type of size distribution.
It has been shown1* that by superposition of two or three log-
normal distributions most aerosol size distributions can be de-
scribed.  For such a distribution a set of parameters has to
be determined, for which the deviation between the simulated
output data of the instrument and the actual measured data be-
comes a minimum.

     A simplex minimization procedure (suggested to us by B.Y.H.
Liu and A. Kapadia) for the EAA, has been chosen to optimize
the distribution parameters.  A modified chi-square with an ad-
ditional weighting function was chosen as an objective function
to characterize the goodness of fit between the simulated and
the measured data.  Starting parameters for the minimization
procedure are estimated from the measured data.  As the optimi-
zation algorithm does not necessarily detect the absolute mini-
mum, several restarts with random variations of the starting
parameters can be done.

INVESTIGATION OF THE EFFICIENCY OF THE DATA REDUCTION PROCEDURE

     A lot of calculations were done to test if this data reduc-
tion procedure works satisfactorily.  In a first step the program
was checked with input data which were simulated from unimodal
and bimodal starting parameters.  The summarized results of these
studies are shown in Table 1.

      In  test  no.  1  the  program  used  fixed  starting  parameters,
which were  not  estimated  from  the input  data.   In  the case  of
the  unimodal  distribution  the  parameters of  the  input distri-
bution were recovered  for  all  considered cases (12  sets  of  param-
eters) .   The  parameters of  the  bimodal distribution were recovered
only in  41% of  a  total  of  243  sets  of distribution  parameters.

      The  calculation of estimates of  the starting  parameters
from the  simulated  input  data  raised  the success  rate for  bimodal
distribution  to 59%.   In  test  no.  3  up to  ten  restarts  with
random  variation  of  the estimated starting parameters in a  range
of  ± 30%  were allowed,  if  the  goodness of  fit  indicated  by  the
absolute  value  of  the  objective function was not  satisfactory.
This finally  gave  a  success  rate  of  94%  which  seems to  be  the
best that could be  achieved  by  this  method.

      In  some  few  of  the successful  cases the actual parameters
of  the  input  distribution were  not  recovered in spite of the
fact that the value  of  the objective  function  indicated  a  very
good fit.  The  recovered  distribution was  compared to the  input
distribution  in a  plot  and agreed nearly exactly,  which  means
that quite  different parameters can describe nearly the  same
distribution.   This  case  only  occurred when  the two distribution
modes  lay close together.
                                192

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     To get results which were closer to reality, in a next step
the simulated input data were slightly varied to simulate random
errors:  12 unimodal and 25 bimodal distributions with ten dif-
ferent sets of errors applied to each were investigated.  In
test no. 4 the errors were equally distributed between 0 and
10%, and in test no. 5 between 0 and 15%.  The success rate in
both cases was 100% for the unimodal and around 85% for the
bimodal distributions.  To test the influence of errors on the
response matrix elements, which could be due to the limited
accuracy of the calibration experiments, calculations were done
with random errors  (0 - 5%) in the matrix elements.  The input
data were free from errors.  The success rate for the unimodal
and bimodal distributions was 100%.

     As a conclusion one can say that the data reduction pro-
cedure works very well in the case of unimodal distributions.
For bimodal distributions several restarts with varied starting
parameters are absolutely necessary to get a considerable rate
of success.  Even then there are cases in which no solution is
found.  With random errors in the input data the success rate
decreases slightly.
        TABLE 1.  RESULTS OF TEST CALCULATIONS FOR THE EAA
        	DATA REDUCTION PROGRAM	

                                                 Success rate
Test no.            Test conditions           Unimodal    Bimodal

    1       Simulated data, fixed starting
              parameters                        100%         41%

    2       Simulated data, starting
              parameters estimated from
              the input data                    100%         59%

    3       Like test no. 2, up to ten
              restarts with random varia-
              tions of the estimated
              starting parameters               100%         94%

    4       Like test no. 3, with random
              errors in the input data;
              errors equally distributed
              between 0 and 10%                 100%         83%

    5       Like test no. 4, errors equally
              distributed between 0 and 15%     100%         85%

    6       Like test no. 3, random errors
              in the response matrix
              elements (0 - 5%)                 100%         100%
                               193

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     When  applying this data  reduction method to  real data, the
random errors  in these data will  make success more  difficult;
the instrument behavior as determined in the calibration experi-
ment may not  be the same for  particles of a shape and material
different  from the calibration  aerosol.

     To eliminate these influences,  a first application check
was done for  a polydisperse DOP aerosol produced  by an atomizer,
Figure 11  shows the results of  this  experiment.   The particle
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                             CHISQ = 0.014

                         — CORRECTED NUMBER DISTRIBUTION

                         P MEASURED DATA

                         • SIMULATED DATA
                0.01
0.1
                            PARTICLE DIAMETER Dp,
                      Figure 11.  Atomizer aerosol (DOP).
                                 194

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number concentration ACN/Alog Dp is plotted against the particle
diameter Dp.  The measured data are represented by squares.
The corrected unimodal number distribution as determined by the
data reduction program is given by the solid line.  The simulated
output data for this distribution, which in the case of an ab-
solute fit had to be identical with the measured data, are given
by circles.  The deviations between measured and simulated data
are in the range of the  instrument's accuracy, which means that
the corrected number distribution represents one possible solu-
tion.  The value of the  objective function is CHISQ = 0.014,
which indicates a good fit, too.

APPLICATIONS OF THE DATA REDUCTION PROCEDURE TO REAL AEROSOLS

     As mentioned above, real aerosols may differ from the cali-
bration aerosols, as far as particle shape, particle material,
and state of the gas are concerned.  For any one of these reasons
the response matrix of an instrument may not be valid for a cer-
tain aerosol which will  cause a failure of the data reduction
procedure.

     In the following, several examples of applying this pro-
cedure to data of different aerosols are given.

     The EAA has been used to determine the particle number dis-
tribution of the aerosol emitted by a spark ignition engine in
connection with studies  to characterize the content of polyaro-
matic hydrocarbons  (PAH) in the particulate matter emitted by
the engine.  Figure 12 shows an example of a size distribution
of this exhaust aerosol.  The solid line gives the bimodal cor-
rected number distribution and the squares represent the measured
data, while the circles  give the simulated data.  As in the
previous example, the deviations between the measured and simu-
lated data are in the range of the instrument's accuracy, which
leads to a rather small  value of the objective function.

     In another study the EAA has been used for the determina-
tion of the size distribution of test fire aerosols.  These test
fires are used to test the reaction of automatic fire detectors.
In Figure 13 the particle number distribution of a smoldering
wood fire aerosol is given.  The fit between the measured and
simulated data is very good; the value of the objective function
is very low.

     The next example,  which is shown in Figure 14, represents
the size distribution of a polyurethane fire aerosol.   In this
case the fit is very bad.  The geometric standard deviation of
the second mode has a value of Oq2 ~ !•!/  which was the lower
limit for  the optimization procedure.   Even with this narrow
distribution the simulated data are more broadly distributed
than the measured data,  which means that for a better fit the
input distribution had to be even narrower.   As it seems very
                               195

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unlikely that a  fire will produce a monodisperse  aerosol,  this

seems  to be a case in which  the instrument's calibration  is  not

valid.   This, however, makes it impossible to find an appropriate

solution with a  data reduction procedure based on this calibra-

tion.
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                   — CORRECTED NUMBER DISTRIBUTION


                    D MEASURED DATA


                    • SIMULATED DATA
                 0.01
                             —i—


                              0.1
                           PARTICLE DIAMETER Dp, fim
          Figure 12. Spark ignition engine exhaust aerosol n = 3000 min~1, X = 0.92.
                                  196

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     In Germany, a certain  type of SiO2 aerosol  is used in test-
ing instrumentation in a dust  tunnel.  The particle mass distri-
bution of  this aerosol has  been determined by  Geipel5 with an
Andersen Stack Sampler.  In Figure 15 his results are shown.
In a first attempt we tried to correct his data  assuming a log-
normal size distribution and using the collection efficiencies
for solid  particles. The resulting log-normal  size distribution
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                 — CORRECTED NUMBER DISTRIBUTION

                  D MEASURED DATA
                  • SIMULATED  DATA
               0.01                   0.1

                         PARTICLE DIAMETER D
                   Figure 13.  Smoldering wood fire aerosol.
                                197

-------
shows  rather good  agreement with  the distribution determined
with sedimentation analysis.   The calculated wall losses (36%)
are also comparable with the ones measured  by Geipel  (38%).
On the other hand  the value of the objective function  is rather
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                     	 CORRECTED NUMBER

                        DISTRIBUTION

                      D MEASURED DATA

                      • SIMULATED DATA
                 0.01
                             0.1


                   PARTICLE DIAMETER D
                                              p/
                       Figure 14. Polyurethane fire aerosol.
                                 198

-------
large  and also  the differences between measured  and simulated

data.   Here again it hasn't  been verified that one can use the
collection efficiencies of  the calibration experiment for  this

real aerosol.
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SUMMARY AND CONCLUSIONS

     Almost all classifying instruments show a certain cross
sensitivity, which can be determined by applying a monodisperse
aerosol.  Knowing the behavior of the instruments one can simu-
late the instrument numerically.  These simulation studies, here
shown for an Electrical Aerosol Analyzer and an Andersen Stack
Sampler, allow us to judge the importance of including real
behavior in the data reduction.  A data reduction program based
on the simplex minimization procedure has been carefully checked.
It has been found that in almost all cases, even if errors are
involved, a solution is found.  In applying it to real aerosols
this data reduction procedure finds its main limitation in the
lack of knowledge about the instrument behavior for the real
aerosol, which may be quite different from the aerosol used in
the calibration experiment.


REFERENCES

1.   Liu, B.Y.H., and D.Y.H. Pui.  On the Performance of the
     Electrical Aerosol Analyzer.  J. Aerosol Sci.  6:249-264,
     1975.

2.   Franzen, H., H.J. Fissan, and U. Urban.    Eichung eines
     Andersen-Stack-Samplers unter Verwendung des Berglund-Liu-
     Generators.  [Calibration of an Andersen Stack Sampler with
     the Use of a Berglund-Liu Generator.]   Staub Reinhalt. Luft
     38:436, 1978.

3.   Gushing, K.M., G.E. Lacey, J.D. McCain, and W.B. Smith.
     Particulate Sizing Devices for Control Device Evaluation:
     Cascade Impactor Calibrations.  EPA-600/2-76-280, U.S. En-
     vironmental Protection Agency, Research Triangle Park, NC,
     1976.  94 pp.

4.   Whitby, K.T.  Modelling of Multimodal Aerosol Size Distri-
     butions.  Presented at the Annual Meeting, Gesellschaft
     fur Aerosolforschung, Bad Soden, Germany, October, 1974.

5.   Geipel, W., and R. Wiedemann.  Erprobung von Emissionsmessver-
     fahren zur Feststellung von Korngrossenfraktionen.   [Tests
     of Methods for Measuring Emissions to Determine Particle
     Size.]  Report No. 7/79.  Lehrstuhl fur Thermische Kraftan-
     lagen, Technische Universitat Munchen.
                               200

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                              PAPER  12


               NON-IDEAL BEHAVIOR IN CASCADE IMPACTORS
                          JOSEPH D. McCAIN
                         JAMES E. McCORMACK *
                     SOUTHERN RESEARCH INSTITUTE


INTRODUCTION

     Cascade impactors have become commonly used measurement
devices for the determination of size distributions of parti-
culate emissions from industrial sources.  Data obtained by means
of impactors are used to characterize emissions from sources,
to determine the performance of particulate control devices,
and in selecting and designing control devices for specific
sources.

     Data provided by impactors are of relatively low resolution
and do not permit the exact reconstruction of the size distri-
bution of the aerosol being sampled, even over the limited range
of sizes nominally covered by most impactors  (approximately 0.5
to 15 jam).  However, little has been done to estimate the magni-
tude of the uncertainties, or errors, which are inherent in the
method insofar as they relate to industrial source emission mea-
surements and determinations of fractional collection efficiencies
of control devices.  The study described here was one with the
specific goals of estimating the effects of two non-ideal operat-
ing characteristics of impactors on the data obtained with them.
These two non-idealities are (1)  the lack of step function stage
collection characteristics and (2)  particle bounce.  Several
authors1'2'3 have proposed various deconvolution procedures which,
when applied to impactor data, would, to a large degree, correct
for the effect of the finite slopes of the stage collection ef-
ficiency curves.  However, little use has been made of these
procedures, primarily because noise in the data frequently results
in oscillatory solutions with large negative values.  In any
case, little quantitative information regarding the magnitude


*Now at the University of Minnesota
                               201

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of the errors introduced by the lack of sharp size cuts in im-
pactors commonly used for stack sampling has been published.
The magnitude of errors introduced by particle bounce has not
previously been quantified at all although the existence of such
errors has been described in the literature. **'5'6'7

TECHNICAL PROCEDURES

     The approach used in this study was the development of a
computer model of cascade impactor performance.  The model was
based on actual impactor performance as measured in a calibra-
tion study of commercially available cascade impactors for stack
sampling.   A total of four simulation models were used for both
a Brink impactor in a commonly used modified configuration for
stack sampling and an Andersen Mark III stack sampler.  The use
of glass fiber collection substrates was assumed for both im-
pactors.  Both greased substrates and glass fiber substrates
are commonly used for sampling at temperatures below 150°C  (300°F)
but no satisfactory greases have been found for use at tempera-
tures over 150°C.  Therefore, glass fiber substrates must usually
be used for collection substrates at elevated temperatures.

     The first model for each impactor was one having ideal col-
lection characteristics, i.e., step functions from 0% to 100%
collection at the stage D50's.   (The stage D50 is that particle
diameter at which the stage has a collection efficiency of 50%.
The D50 is generally used as the characteristic cut off diameter
for particles collected by the stage.)  This model was used as
a performance standard against which the remaining three models
could be compared and also provided a basis for checking the
program.

     The assumed operating conditions and resulting cut sizes
(Dso's) of the two impactors modeled in the study are given in
Table 1.  The models of the Brink impactor  included a cyclone
precollector which was assumed to have the  same performance
characteristics in all three of the simulations other than that
of the "IDEAL Brink."  The cyclone performance was based on
calibration data for a cyclone in common use with the Brink im-
pactor in a modified configuration for stack sampling.  This
cyclone had a collection efficiency of 100% for particles larger
than about 20 ym.

     The second model for each impactor utilized the actual cali-
bration data for each stage.  In this model the stage collection
efficiencies increased monotonically with increasing Stokes1
numbers  (increasing particle size) to a maximum value of about
90% to 95%.  The efficiencies then decreased for larger Stokes1
numbers to a value of 35% to 40% and remained constant there-
after.  A composite of the calibration data for stages two  (2)
through seven  (7) of the Andersen impactor, which illustrates
                               202

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      TABLE 1.   SIMULATION CONDITIONS OF THE MODELED IMPACTOR
                            PERFORMANCE
Temperature, °C  (°F)
Gas composition
Particle density, g/cm3
Flow rate, alpm  (acfm)
Barometric pressure, mm Hg

Stage/D50(ym)
   Brink

177 (350)
Standard air
  2.27
  1.13 (0.040)
749
  Andersen

177 (350)
Standard air
  2.27
 17.0 (0.600)
749
1
2
3
4
5
6
7
8
9.
6.
3.
1.
1.
0.
0.
0.
60a
18b
39
85
23
905
589
198b
7.84
7.40
4.44
2.87
1.58
0.855
0.449
0.200

a Stage 1 is a
Stages 2 and
cyclone precollector .
8 are part of the modifications
to the impactor.
the behavior described above, is shown in Figure 1.  Data for
stages 1 and 8 were offset from the tight grouping of the data
for the remaining stages and hence were omitted in Figure 1 for
purposes of clarity in illustrating the behavior trends of the
stage efficiency curves.  The data for the Brink impactor ex-
hibited similar trends.  This model, Model 2, is called the
"Normal Bounce" model.

     The third model was identical to the second except that
the rollover and decline in efficiency for larger Stokes1 num-
bers was ignored.  Instead, the efficiencies were assumed to
smoothly increase to 100% and remain at that value for increas-
ingly larger Stokes1 numbers.  This is called the "No Bounce"
model.  The fourth model was also identical to Model 2 with the
exception that the collection efficiencies were assumed to drop
rapidly to a value of 2% for Stokes1 numbers larger than that
at which the collection efficiency reached a peak in the cali-
bration data.  This model was termed the "Extreme Bounce" model.

     The use of the same basic collection efficiency curves for
the "No Bounce", "Normal Bounce", and "Extreme Bounce" models
for particle sizes smaller than those for which the collection
efficiencies were maximal in the calibration data is probably
a realistic representation of the actual performance of the im-
pactors in collecting various types of particles.  Rao5 found
that impactor collection characteristics for dry solid particles
                               203

-------
and oil particles  were virtually identical  when  glass fiber sub-
strates were  used  for  Stokes1 numbers smaller  than those at which
the peak efficiency was reached for the dry solid particles.
Beyond this point  he found that oil particles  were collected
with efficiencies  which increased to 100% with increasing Stokes'
number while  the efficiencies declined for  the dry particles
as a result of  bounce.  Figure 2 shows an example of the four
modeled collection efficiency characteristics  of one stage of
the Andersen  impactor.

RESULTS AND DISCUSSION

     The performance of each model of the two  impactors was
evaluated  for aerosols having log-normal size  distributions with
mass median diameters (MMD) of 1.5, 2.6, 4.5,  7.8, 13.5, and
27 micrometers.  Geometric standard deviations,  ag, of 2, 3,
and 4 were used at each particle size.  Because or the volume
of the data generated only representative results are presented
in this paper.
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                                                         10.0
                                                           4181-141
     Figure 1. Composite of calibration data for the Andersen impactor, stages 2 through 7,
                                204

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     Figures  3  through 6 show  typical results  for  the two im-
pactors  in  a  cumulative percentage presentation.   It is evident
from all  four of these figures that particle bounce severely
distorts  the  size distributions,  especially for  aerosols having
large mass  median diameters.   Figures 3 and 4  show the results
of the simulations for the  same impactor and size  distributions,
the difference  between the  two being the omission  of the back-
up filter catch in presenting  the results in Figure 4.  Comparison
of Figures  3  and 4 indicates  that omitting the back-up filter
in calculating  the cumulative  percentages greatly  reduces the
distortion  resulting from bounce.  Comparison  of Figures 3 and
5 shows  that  increasing the width of the input size distribution
(increasing ag) reduces the distortion caused  by bounce although
the distortion remains appreciable for the extreme bounce models
at large  HMD's.
   100 —
                           5        10       20


                           PARTICLE DIAMETER, ^m
100
                                                              4181-142
           Figure 2. An illustration of the four modeled stage collection efficiency
                  curves of a typical stage of the Andersen impactor.  Model 1 is
                  the ideal behavior model, model 2 is the normal bounce modelt
                  model 3 is the no bounce model, and model 4 is the extreme
                  bounce  model.
                                 205

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                                              1.0
                                   PARTICLE DIAMETER,
                                                                                10.0
                                                                                  4181-143
      Figure 3. Recovered particle size distributions on a cumulative percentage basis from
               the Brink impactor models for og = 2.0 and mass median diameters of 1.5,
               4.5, 13.5, and 27 urn.  The heavy fines represent the input distributions.
                                         206

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4181-144
     Figure 4.  Recovered particle size distributions on a cumulative percentage basis from the

              Brink impactor models shown in Figure 3 with backup fitter catches omitted

              from the analysis.  The heavy lines represent the input distributions.
                                          207

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                                                                                     10.0
                                                                                   4181-145
      Figure 5. Recovered particle size distributions on a cumulative percentage basis from the
               Brink impactor models for Og = 3.0 and mass median diameters of 1.5, 4.5,
               13.5, and 27 fj.m (backup filter included in the analysis).  The heavy lines
               represent the input distributions.
                                          208

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                                                                                 4181-146
   Figure 6.  Recovered particle size distributions on a cumulative percentage basis for the
             Andersen impactor for OQ = 2.0 and mass median diameters of 1.5, 4.5, and
             13.5 yjn.  The backup filter was excluded from analysis in the results shown.
             The heavy lines represent the input distributions.
                                         209

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     Figure 6 shows the results from the Andersen models corre-
sponding to three of the four cases for the Brink model shown
in Figure 4.  Note that the deviations from the input distri-
bution resulting from bounce are more severe in the Andersen
results than in the Brink.  This difference in the severity of
the distortions apparently results from the cyclone precollector
on the Brink which removes most of the large particles which
are responsible for raising the apparent percentages of fines
in the recovered size distributions.

     It should also be noted that the relative errors in mass
median diameters become increasingly large as the MMD of the
input aerosol decreases.  The recovered MMD's were found to be
systematically large for test aerosol MMD's below 10 ym.  The
values of ag were also systematically high with larger relative
errors at the lower values of og, as would be expected because
of the low resolution afforded 5y impactors.

     In many cases (e.g., control device fractional collection
efficiency studies) the slope of the size distribution curve,
expressed in mass concentration units, is the quantity of greatest
interest.  The most common manner of presentation of this slope
is of the form dm/dlogD versus diameter  (units of mass concentra-
tion) .  The quantity dm/dlogD is often approximated directly
from the impactor data, stage by stage, as Am^/logD^, where

     Am^ = mass concentration of particles retained by the  ith
     stage
                    and AlogD. = log —77;—:	  .
                              1         (DsoJi

The particle diameter is then taken to be the geometric mean
of (DSQ)..^ and (Dgo).^ or

                    Dg = (Dso^ x  (D50)i_1

     Figures 7 and 8 illustrate recovered size distributions
presented in such a manner, together with the input distribu-
tions, for representative sets of Brink and Andersen results.
The results for the "extreme bounce" case are not shown in Fig-
ures 1 and 8 but the values in those cases generally fall between
the "no bounce" and "normal bounce" cases except for the back-
up filters, for which the values were much higher in the "extreme
bounce" case than in the other two cases.  Except for the finest
size fractions, represented by the back-up filter catches, and
the fine fraction tails of the low ag distributions, the agree-
ment between the recovered values of  (Am/AlogD)^ generally lie
reasonably close to the input distributions.  However, errors
of up to ±35% are not infrequent.
                                210

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                                                 A NORMAL BOUNCE
                         10'°              101  10'1             10"°
                          GEOMETRIC MEAN DIAMETER, micrometers
                                                                           4181-147
Figure 7. Recovered particle size distributions on a differential basis from the Brink impactor
         models for mass median diameters of 4.5 and 27 JU/T? and Og's of 2 and 3.
         The heavy curves represent the input distributions.
                                        211

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                                   •II1
                                 O NO BOUNCE
                                 A NORMAL BOUNCE
   i
-------
     Tables 2 and 3 show the errors, expressed as percentages,
in the recovered values of (Am/AlogD)i for several cases for
each of the two impactors.  (For the purpose of calculating log
D and D for the filter catches, it was assumed that the diameter
range covered by the filter was (D50)8 down to %(D50)8.

     Although no results for ag = 4 have been shown, the agree-
ment between the recovered size distributions and the  input dis-
tributions was progressively better as ag increased and was quite
good in all cases for ag = 4 with the exception of back-up filter
catches when bounce was present.

     Table 4 shows the percentages of cases in which the recovered
value (Am/AlogD)£ lay within factors of 1.2, 1.5, and  2 of the
true value.  From these results it appears that the concentra-
tions of fine particles as measured with impactors can seldom
be taken to be known better than to within a factor much smaller
than 1.5 unless the particles are known to be adhesive or an
effective adhesive coating can be applied to the substrates.
      TABLE 2,   PERCENT ERRORS IN Aitl/AlogD, ANDERSEN IMPACTOR
                     No Bounce
MMD

Stage/Error
 F
 8
 7
 6
 5
 4
 3
 2
1.5


144
  9
 -8
-18
-14
  6
    4.5        13.5
     56
     13
    -19         18
    -26        -20
    -19        -30
    -23        -28

Normal Bounce
1.5


 22
-14
-11
-10
-12
 -7
 10
  9
4.5


 38
 -5
 -4
 -8
-17
-21
-15
-22
13.5
  4
-24
-25
  0
-24
F
8
7
6
5
4
3
568
22
-6
-20
16
5

121000
920
111
9
-18
-27
-20



293
39
-17
-30
44
-12
-11
-12
-12
-7
9
173
8
1
-11
-16
-21
-16
1720
103
37
4
-11
-24
-25

NOTE:  Values are omitted  for  stages  for  which  the  collected mass
       would be too small  to be detected  in  field sampling  programs,
                               213

-------
       TABLE 3.  PERCENT ERRORS IN Aro/AlogD, BRINK IMPACTOR
                   No Bounce
HMD
Stage/Error
 F
 6
 5
 4
 3
 2
 1
1.5   4.5   13.5
220
 -6
-43
-19
-15
 -1
 88
220
-35
  3
 -3
-10
-14
             27
 84
 -8
-15
33
 7
1.5


 24
-37
-32
 -9
 -4
  4
 34
                        4.5   13.5
 53
-21
-39
-12
 ~9
-20
 -3
 13
-40
 -5
 -3
-23
-14
                                                              27
-37
  4
  8
-22
-14
                     Bounce
F
6
5
4
3
2
1
550
-10
-40
-20
-16
-1
86

238
-8
10
-4
-28
-15




107
7 100
-18 3
41
-39
-29
-10
-4
4
33
123
-24
-33
-12
-10
-18
-4

12
-26
0
-3
-20
-16


-10
17
10
-16
-17

NOTE:  Values are omitted for stages for which the collected
       mass would be too small to be detected in field sampling
       programs.
      TABLE 4.  PERCENTAGE OF TRIAL CASES IN WHICH RECOVERED
            VALUE  OF  (Am/AlogD)  IS  WITHIN THE INDICATED
                     FACTOR OF THE TRUE VALUE
                  Andersen
                                           Brink
Factor
Stage/Percent
  of cases
  1.2
  1.5
  2.0
    Factor
    Stage/Percent
      of cases
         1.2  1.5  2.0
F
8
7
6
5
4
3
2
0
57
65
65
75
30
40
(30)
31
71
76
80
100
100
90
(90)
38
79
82
90
100
100
90
(90)
F
6
5
4
3
2
1

0
35
11
80
74
42
71

33
59
47
95
91
96
72

56
82
100
100
91
100
100


Andersen table covers all cases
with HMD = 1.5, 2.6, 4.5, 7.8,
13.5 and ag = 2, 3
for both normal bounce and no
bounce
                        Brink table covers all cases
                        with HMD = 1.5, 2.6, 4.5, 7.8,
                        13.5, 27 and ag =2, 3
                        for both normal bounce and no
                        bounce
                               214

-------
     There  is  some  evidence,8'9  although  it  is  not  conclusive,
that the use of  adhesive coatings  (greases)  on  the  substrates
may become  ineffective as  the particulate deposits  build  up  under
the impactor jets.  This would result  in  the same type  of errors
due to particle  bounce resulting in  back-up  filter  contamination
by oversize particles with greased substrates as has  been shown
to occur with  glass fiber  substrates.
CONCLUSIONS AND RECOMMENDATIONS

     From the evidence presented here, it  is suggested  that  back-
up filter catches generally should be omitted  from data presenta-
tion when dry, non-sticky particulates are sampled.  Exceptions
should be made only if the MMD is smaller  than about 2.5  ym.
In addition it is suggested that cyclone precollectors  having
D50's somewhat larger than the first impaction stage D50  be  used
whenever a non-sticky particulate is sampled.  The use  of such
cyclones tends to greatly reduce errors due to particle bounce.

ACKNOWLEDGEMENT

     The work reported here was done under support from the  In-
dustrial Environmental Research Laboratory of  the U.S.  Environ-
mental Protection Agency; Contract No. 68-02-2131, D.B. Harris,
Project Officer.
REFERENCES

1.   Cooper, Douglas w., and John W. Davis.  Cascade Impactors
     for Aerosols:  Improved Data Analysis.  Am. Ind. Hyg. Assoc,
     J. 33(2):79-89, 1972.

2.   Cooper, Douglas W., and Lloyd A. Spielman.  Data Inversion
     Using Nonlinear Programming with Physical Constraints:
     Aerosol Size Distribution Measurement by Impactors.  Atmos.
     Environ. 10(9):723-729, 1976.

3.   Picknett,  R.G.   A New Method of Determining Aerosol Size
     Distributions from Multistage Sampler Data.  J. Aerosol
     Sci.  3:185-198, 1972.

4.   McCain, J.D., K.M. Gushing, and W.B. Smith.  Methods for
     Determining Particulate Mass and Size Properties:  Labora-
     tory and Field  Measurements.  J. Air Pollut. Control Assoc.
     24(12):1172-1176, 1974.

5.   Rao,  A.K.   An Experimental Study of Inertial Impactors.
     Ph.D. Dissertation, University of Minnesota, Minneapolis,
     1975.
                               215

-------
6.   Dzubay, T.G.,  L.E. Hines, and R.K. Stevens.  Particle Bounce
     Errors in Cascade Impactors.  Atmos. Environ. 10(3):229-
     234, 1976.

7.   Natusch, D.F.S., and J.R. Wallace.  Determination of Air-
     borne Particle Size Distributions:  Calculation of Cross-
     Sensitivity and Discreteness Effects in Cascade Impaction.
     Atmos. Environ.  10(4):315-324, 1976.

8.   Gushing, K.M., J.D. McCain, and W.B. Smith.  Experimental
     Determination of Sizing Parameters and Wall Losses of Five
     Commercially Available Cascade Impactors.  Annual Meeting,
     Air Pollution Control Association, Paper No. 76-37.4, 1976.

9.   Lundgren, D.A.  An Aerosol Sampler for Determination of
     Particle Concentration as a Function of Size and Time.
     J. Air Pollut. Control Assoc. 17(4):225-229, 1967.
                             216

-------
                             PAPER 13
    FIELD TESTING OF AUTOMATIC PIEZOELECTRIC MICROBALANCES FOR
         OUTDOOR  AEROSOL MASS  CONCENTRATION MEASUREMENTS
                        KAZUO TSURUBAYASHI
                           HAJIME  KANO
                   NIHON KAGAKU KOGYO CO., LTD.
ABSTRACT

     The main purpose of this paper is to describe the perform-
ance, 'field-testing data, and sampling technique of an automati-
cally operated  piezoelectric microbalance particle mass concen-
tration monitor (automatic piezobalance) which has high sensi-
tivity for particle detection.  A further application, real-time
particle size measurement using an Andersen cascade impactor,
is also described.

     Results presented here show a high correlation coefficient
(greater than 0.9) between the automatic piezobalance and low
volume sampling and filter weighing (LV) measurements when the
sampling conditions are set up to avoid wind effects and to mini-
mize wall losses of particles in the sampling tube.

INTRODUCTION

     The Japanese law for ambient air quality standards specifies
that:
     1)  Regulations must be established based upon the mass
         concentration of respirable particulate matter  (defined
         as airborne particles smaller than approximately 10 urn),

     2)  The standard value of respirable particulate matter
         for the environment should be less than 0.1 mg/m3, when
         one-hour values are averaged over a 24-hour period,
         and less than 0.2 mg/m3 for each measured one-hour
         value.

     3)  Low volume sampling, using a 10 ym cut-off device and
         a filter weighing method, should be the standard mea-
         suring method.
                               217

-------
Light-scattering dust meters have been accepted for measuring
one-hour values only if they have been first calibrated at each
local monitoring station.

     Monitoring and surveillance of ambient air quality is being
done by the National Air Monitoring Network and city or prefec-
tural monitoring stations.  There are more than 1000 such sta-
tions in Japan.  However, ever since the law was enacted, the
standard measuring method has had two main problems that still
remain unsolved:

     1)   One-hour values of mass concentration cannot be measured
         by the LV method, and

     2)   Light-scattering measurements do not correlate well
         with LV measurements.

     A wide range of people have requested improvement of the
standard measuring method.  In 1976, the automatic piezobalance
(Piezobalance is a trademark registered in the USA by TSI In-
corporated) was developed to solve these problems.  The Japanese
Environmental Agency has field tested several automatic piezo-
balances and several beta absorption instruments as alternative
measurement methods.

PRINCIPLE AND OPERATION

     The automatic piezobalance, shown schematically in Figure
1, consists of a mass-sensing/auto-cleaning system and a digital
processing system.  The mass-sensing/auto-cleaning system in-
cludes a vacuum pump with one 5,/min sonic nozzle, an automatic
crystal (sensor) cleaner, an analog sequence controller, a pre-
cipitator with removable precipitation needle, a detecting crys-
tal with oscillator and mixing circuit, and an impactor.  The
digital processing system includes a timer-controller, LED dis-
play, and a printer that prints data, time, mass concentration,
and mixed crystal frequency.

     The aerosol sample is drawn into the 10-ym impactor at a
flow rate of 1.0 8,/min by a vacuum pump.  The impactor removes
aerosol particles greater than 10 vim (aerodynamic particle diam-
eter) .  Particles smaller than 10 ym are carried by the air to
an electrostatic precipitator which deposits them onto a mass-
sensing piezoelectric crystal oscillating at its natural fre-
quency.   The mass of particles on the crystal sensor causes the
oscillation frequency to decrease by an amount proportional to
the mass of particles.  Every 10 seconds, when the instrument
is operating in the check mode, the frequency change is detected
by a counter and displayed on the digital readout.  Every 120
seconds, when the instrument is operating in the measurement
mode, the frequency change from the starting frequency is con-
verted by a digital processor to mass concentration in units
of yg/m3 and displayed on the readout as shown in Figure 2.
                               218

-------
to
                    r
                    i
                                          Sampling air

                                          _
IMPACTOR


<

>

.. Precioitator
& crystal

TF
I



it
»

rixh
Cleaning I S\
Mechanismj Fllter VX
© 0-
r!
f
Son
^r
r
i
i
i
L
c
H.V.

OSC.
j
r
Processor
I/O

nozzle
-)
1
1
1
                       Mass sensing and auto-cleaning
Digital processor.
Printer
                                          Figure 1.  Schematic diagram of automatic Piezobalance.

-------
CLEANING FOR TWO MINUTES

           fmax
                                      	-/	.
MEASURING FOR 28 MINUTES
                                                                                       NOT MEASURING
to
10
o
                                                               CLEANING & PRINT OUT
                                                                                                              Cj = a(fi-fo)tx
                                                                                                              fi:  frequency shift at time tx
                                                                                                              fo: starting frequency
                                                                                                              a:  mass concentration coefficient
                                                                                                             Ci_i4 : average concentration in 0-28 min
                                                                                                             C2-14 : average concentration in 30-58 min
                                                                                                             Chr = (C1-14 + C2-14)/2
                                                                                                             Cnr : one hour value in 0-60 min
                                                   Figure 2. Measuring system of automatic Piezobalance.

-------
     The concentration C. at  each  sampling  time  t.  is  expressed
by                       x                         x
         Ci =     t.    «                                      <


where

         f. is the  frequency at sampling  time  t.

         f  is the  starting frequency

         a is the mass concentration coefficient.

The displayed concentration then  is the average value of  all
120-second measurements from the  start until the end of the
sampling time.

     After a sampling time of 28  min, a cleaning command  signal
is emitted.  The last 2 min of the 30-min cycle are used  for
cleaning and drying the crystal sensor.

     The one-hour concentration value is  the average of the
values obtained during the first  and the  second 30-min periods
(28 min and 58 min  after t^ = 0) .  The one-hour value is  cal-
culated automatically as defined  by Equation 2:


         Chr = (C1-14 + C2-14)/2

         Cl-14 is the avera9e concentration during t. =0-28 min

         C2-14 is the avera9e concentration during t. =30-58 min

         C^r is the one-hour value during t. =0-60 min

The time and concentration are printed every 30 minutes.

     After the printout, the automatic cleaning cycle begins.
The crystal is first washed with  a detergent,  then rinsed and
dried.  After 2 min, the crystal  is dry and measurement begins
automatically.

     When something goes wrong during a measurement cycle, such
as loss of precipitator current,  an alarm lamp turns on and the
instrument automatically stops the measurement to avoid record-
ing erroneous values.

CALIBRATION

     The crystal mass  concentration coefficient, a, in Equation 1
could be calculated precisely from the basic theory of piezo-
electricity if we assume ideal particle collection and sensing

                               221

-------
efficiency and if the particles are assumed to be deposited uni-
formly over the entire vibrating surface of the crystal.1'2  How-
ever, the automatic piezobalance requires experimental calibration
for an accurate determination of the coefficient a for the fol-
lowing reasons:

     1)   Aerosol particles are not deposited in a uniform layer
         over the entire electrode, making the mass sensitivity
         and particulate deposition profiles important.

     2)   Particle collection and sensing efficiencies, though
         repeatable, are not precisely known for each instrument,
         each precipitator needle, or each type of airborne par-
         ticle.

     3)   The shape and size of the crystal electrode and the
         thickness of the crystal are not precisely known for
         a given sensor.

     Therefore, we have set up a calibration procedure to experi-
mentally determine the value of a for a standard aerosol similar
to outdoor airborne particles.  Figures 3 and 4 show the systems
used to calibrate the automatic piezobalances with smoke, KC1,
and PbCl2 aerosols.2'3  The basic technique is to adjust the piezo-
balance sensitivity until its concentration measurements agree
with low volume filter concentration measurements while both
are sampling from a common aerosol source.

     The aerosol used for calibration is drawn through an impactor,
usually with 10-ym cut size, and into a manifold where the aerosol
is mixed and electrostatically neutralized.  Several automatic
piezobalances and two low-volume filter samplers, arranged nearly
symmetrically around the manifold, sample simultaneously from
the manifold.  No significant variation has been found between
sampling ports.  The automatic piezobalance flow rate (1.0 &/min)
is maintained constant by its pump.  The low-volume filter flow
rate (15 &/min) is continuously monitored by the operator and
maintained constant by manual adjustment.  The 47-mm filters
in the low-volume sampling systems are either silver membrane
or glass fiber filters in a tight filter holder.  The filter
material does not gain or lose significant weight as the relative
humidity changes.  Since the particles deposited on the filter
usually do gain or lose moisture as relative humidity changes,
the filters are weighed immediately after the sampling period
at the existing relative humidity in the sampling room.  The
weighing uncertainty of the gravimetric microbalance is about
±5 pg.   The sample period is 0.5 - 2.0 hr, collecting approxi-
mately 100 - 3000 yg of particles on each filter.  The average
of the automatic piezobalance measurements, made once every 2
minutes throughout each filter sample, is then compared with
the corresponding low-volume filter measurements.
                               222

-------
                                      TOP VIEW
          THERMOMETER
                                       BALL
                                       VALVE  FILTER   FLOWMETER
                                  REGULATOR
                                  VALVE
     AEROSOL INLET PORT

PIEZOBALANCE
EXHAUST RETURN PORT
                                               VACUUM
        AUTOMATIC
        PIEZOBALANCE
                                           AUTOMATIC PIEZOBALANCE
          PRE-RUN
          SUCTION PORT
                                         VALVE FILTER FLOWMETER VALVE
                  '!'v
                 '  <•__   S
               CHAMBER
                 \u
                               SIDE VIEW OF MANIFOLD

                             MIXING FAN

                                           30LPM
J}
                                     PIEZOBALANCE
                                    • EXHAUST RETURN PORT
                                                                        10 Jim IMPACTOR
                 ,'   \.  I  If   ^ y
                '    . iTt  .  V
                >* 
-------
AUTOMATIC PIEZOBALANCE
                                                                                  FILTERED DILUTION AIR
                                                                                       FUME GENERATOR
                           Figure 4. Calibration system of Piezobalance by fume aerosols.

-------
     Figures  5  and 6 show the result  of mass sensitivity calibra-
tions obtained  using the system  shown in Figures 3 and  4.

     Figures  5  and 6 show that the  experimental sensitivity a
for the tested  aerosol is within ±  10% of the theoretical value
calculated  by assuming ideal particle collection, deposition,
and sensing.  The data also show good linearity up to concentra-
tions at  least  as high as 1500 yg/m3.
                 40 -
                 30 -
           GO
           LLJ
           O
           CQ
           O
           N
           nc
           LLJ
           CQ
           5
           D
20  -
10 -
                    10   864202   468  10
                              MASS SENSITIVITY ERROR, %    (+)
               Figure 5. Experimental result of mass sensitivity test.
                                 225

-------
FIELD TESTING

     After  finishing  the  sensitivity calibrations in  the  labora-
tory, a  pair of automatic piezobalances  with mass concentration
coefficients adjusted  to  the theoretical sensitivity  (180 Hz/yg)
were tested at two local  pollution monitoring stations  in Japan.
The main purposes of  the  field test were:

     1)   To evaluate  the  variation in measurements between two
          automatic piezobalances for one-hour values  and  24-hour
          averaged values.
           1500
   CO
   .E
    O)

   LU
   o
   CO
   O
   N
   LU
o


IT
I-

LU
O
2
O
O
   LU
   _i
   O
   1-
   DC
           1000
           500
                  O   AUTOMATIC


                  A   PORTABLE
                                           O  A   PbCij FUME

                                           O  A   KCI FUME

                                           O  A  SMOKE PARTICLE
                             500
                                           1000
1500
                             FILTER CONCENTRATION,Atg/m3
             Figure 6.  Experimental result of mass sensitivity calibration.
                                 226

-------
     2)  To  evaluate the correlation  between the mass concentra-
         tion  measured by LV method and  the concentration mea-
         sured by automatic piezobalances.

     3)  To  evaluate possible variations  in sensitivity for par-
         ticles at each local pollution monitoring station.

     4)  To  evaluate the resolution necessary to accurately
         measure mass concentration,  within a one-hour period.

     5)  To  evaluate the effects of atmospheric conditions,
         especially relative humidity.

     Figure  7  shows the experimental  setup  for the automatic
piezobalances  at the pollution monitoring station.  Two automatic
piezobalances  were placed in the measuring  room beside other
pollution measuring instruments, i.e., S02  monitors, NOX monitors,
light scattering dust meters, etc.  Two  low-volume samplers were
set on the roof of the measuring room near  the inlet of the air
sampling manifold.
                       L.V. SAMPLER 1  L.V. SAMPLER 2
  EXHAUST AIR
                                                           SAMPLING
                                                           AIR
                                 f  f v

                               S02 METER
                               NOx METER etc.
                                            WULCL
                  LIGHT SCATTERING
                  DUST METER
                  AUTOMATIC PIEZOBALANCES
                       POLLUTION MONITORING STATION
            Figure 7. Experimental set up at the pollution monitoring station.
                                227

-------
     Airborne particles  were sampled at a flow  rate  of  approxi-
mately 150 &/min.   The  inlet of the air sampling manifold was
located more than  10  m  above ground level.  The air  velocity
at the sampling  points  to all the instruments was  about 0.5 m/s.
Polyethylene tubing with 0.375-inch I.D. carried the sampled
air between the  manifold and the automatic piezobalances.  A
branch fitting near the  automatic piezobalances split the air
sample to the instruments.

     The experimental results are shown in Figures 8, 9,  and 10.
Figure 8 is the  correlation between LV measurements,  which sampled
the air for two  or three days, and the average  automatic piezobalance
value for the corresponding sampling time.  Figure 8 shows that
the correlation  coefficient is greater than 0.9 at every monitor-
ing station.  It also shows that the theoretical sensitivity
coefficient  (180 Hz/yg)  used for all instruments was valid within
± 20% at every monitoring station.
    CO

     D)
     a.
    z
    LJJ
    O
    2
    O
    O
    LLJ
    O
    CD
    O
    N
    UJ
          120
100
           80
60
40
           20
0

A

•

Y =
7 =
y =
7 =
y =
7 =
1.08x + 4.76
0.940 ( KAN AGAWA)
0.935x + 4.39
0.984 (SUITA)
0.954x- 1.53
0.908 (SAPPORO)
                   20
               40
60
80
100
120
                                                        140
                      LOW VOLUME FILTER CONCENTRATION,
             Figure 8. Comparison of L V. filter and Piezobalance concentrations.
                                228

-------
     Figures  9  and 10 show the relationship between two automatic
piezobalances for  24-hour averaged values and one-hour measure-
ments, respectively.   The indicated  difference between two auto-
matic piezobalances was ± 5 ug/m3 ±  10%  of measured value for
one-hour measurements and ± 5 yg/m3  ±  5% for 24-hour averaged
values.  The  data  also shows that the  automatic piezobalance
has high resolution,  better than 10  yg/m3, for one-hour mass
concentration measurements of ambient  atmospheric aerosol in
actual field  situations.

     Daley  et al.1* have investigated experimentally the effect
of humidity changes on the indicated mass deposit for several
          CO


           §

          Z
          O
           cc
           I-
          o
          •z.
          o
          o
          CM
          6
          z
          LLJ
          O
          CO
          O
          N
          UJ
               100
80
60
40
               20
                        20
                               40
                       60
                              80
100
                        PEIZOBALANCE NO. 1 CONCENTRATION, j/9/m3
      Figure 9. Comparison of two automatic Piezobalances for 24 hour averaged values.
                                229

-------
aerosol particles.   Figure 11 shows  the  experimental setup for
measuring  the  humidity effects at the  field testing stations.
A diffusion  aerosol dryer, which can reduce humidity from 80%
to 40% RH, was installed at the inlet  of one of the automatic
piezobalances.   Measurements were made at 24 to 35°C, 70 to 92%
RH.  The results of the experiment are plotted in Figure 12.
As shown,  in the concentration range below 60 ng/m3, there is
no significant difference between the  two automatic piezobalance
indications.   However, at concentrations greater than 60 ug/m3,
the indication of the automatic piezobalance without the dryer
increases  compared  with the automatic  piezobalance with the
dryer.
     01

      O)

     zf
     O
Ill
O
O
O
CM
d
2:
uj
o
     CD
     O
     N
           160
      140
           120
           100
            80
      60
            40
            20
                   20
                   40
60     80    100    120    140    160
                      PIEZOBALANCE NO. 1 CONCENTRATION,
    Figure 10.  Comparison of two automatic Piezobalances for one hour measurements.
                                230

-------
CONSIDERATION OF  THE  SAMPLING SYSTEM

     The automatic  piezobalance was designed for stationary  opera-
tion at fixed pollution  monitoring stations.5"7  It has  a  sampling
flow rate of 1.0  fc/min.   For the airborne particle measurements,
we must carefully design the sampling system to avoid wind-induced
losses near the inlet of the sampling tube and to minimize wall
losses in the sampling tube.

     Figure 7 shows one  of  the most common sampling systems  used
at monitoring stations in Japan.   In this case, it is necessary
to use the shortest possible length of horizontal sampling tube
between the sampling  manifold and the instruments to avoid the
above mentioned particle losses.
                 10 L CHAMBER
      THERMOMETER
      HYGROMETER
                                                       PIEZOBALANCE
            Figure 11.  Experimental set-up to check the effect of humidity.
                               231

-------
     Figure  13  shows the relationship between the horizontal
length of sampling  tube in centimeters  and  the particle deposi-
tion rate in  percent.   The calculation  was  made for a flow rate
of 2 £/min with 1/2-in. I.D. tubing  for various particle diameters
(in micrometers)  using an equation described by Pich.8

     During  the field  tests, especially on  windy days, there
was a large  difference between LV measurements and automatic
piezobalance  measurements.  Deposition  losses in the sampling
tube can account for these observed  differences.

           £E
           O
           I-
           D
           O
           I
           CN

           d
           LLJ
           O
           00
           O
           LU
           51
                100
80
60
               40
               20
                        20
               40
60
80
100
                      PIEZOBALANCE NO. ^ (WITH DRYER), jug/m3
                    Figure 12.  Effect of humidity on Piezobalance.
                                232

-------
     Figure 14  is  a  schematic diagram of the isokinetic  total
and respirable  particle  sampler (Isokinetic TR Sampler).   This
sampler was designed to  avoid the losses noted above.  The sampler
consists of a sampling nozzle; an impactor which can  deposit
large particles on a filter  for weighing; a filter holder  with
a hole in the center to  allow part of the respirable  particles
to collect on the  filter and part of the same sample  to  be di-
rected to the automatic  piezobalance.

     This sampler  can also be used for dynamic calibration to
measure precisely  the mass concentration coefficient  for  actual
airborne particles at any monitoring location.  Figure 15  shows
a dynamic calibration setup using this sampler.  As shown  in
the figure, one can  supply test aerosol to the TR Sampler  and
automatic piezobalances  either from a standard particle  generator
or from outdoor air.  Figure 16 shows the data for a  dynamic
calibration with a particle generator.  The data show a  very
high correlation between LV measurements and the measurements
made with the automatic  piezobalances.
             100
          5?

          uT
          K

          DC

          Z
          O


          I   50
          Q.
          LU
          Q
          UJ

          O
       8pm
                                              7/im
                                                6/im
                         100
200
                                                     400
                     HORIZONTAL LENGTH OF SAMPLING TUBE, cm
        Figure 13.  Relationship between tube length and particle deposition rate.
                                233

-------
to
CO
               MESH
                         AEROSOL INLET

                                1
rv.
F
\
LJ.
.*-

±=
L
^x


1
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/
^


MBMMM
1 LP^
FILTER
^ 	 FILTER
- 20 LPM
>
I 	
/I
                                                      V.P.
                                                                    100
                                                                 o
                                                                 ^
                                                                 oc
50
                                                                                      I    i   i  I  i .  • . I
                                                                      0.5       1                5       10


                                                                                  PARTICLE DIAMETER, Aim
                                            30
                          PI EZOBALANCE
                                      Figure  14.  Schematic diagram of Isokinetic TR Sampler.

-------
OTHER APPLICATIONS

     When  studying hazardous effects to the human body  caused
by respirable  particles and controlling the source of these
aerosol pollutants,  it is becoming more important to measure
the mass concentration and size distribution of airborne  par-
ticles smaller  than 10 ym.  At present, it takes one to two weeks
to get enough  samples  in certain size ranges to accurately weigh
using an inertial  sampler such as a cascade impactor.9

     An automatic  piezobalance can make near real-time  measure-
ments of the mass  concentration within size ranges determined
by an inertial  sampler.   The experimental setup for measuring
the real-time mass concentration as a function of particle size
is shown in Figure 17.   An Andersen ambient air sampler,  modified
by making  a sampling hole in the side wall of each stage, was
used for sizing the particles.   Airborne particles were sampled
by the automatic piezobalance through the side wall sampling
tube at each stage of  the Andersen sampler at a flow rate of
1.0 £/min.
                                                         OUTDOORS
                   VACUUM
                   PUMP
SAMPLING TUBE
                       CHAMBtIR
                                               TR
                                               SAMPLER
AEROSOL GENERATOR
    PIEZOBALANCE
                                                           AIRBORNE
                                                           PARTICLES
             Figure 15.  Dynamic calibration set-up using TR Sampler.
                               235

-------
                 n


                  O)
                  3.
       1500
tsj
U)
cc
H
Z
LU
o


I
LU
0
                        1000
                 CQ
                 O
                 N
                         500
                                             500
                                                   Ser. No.


                                                  ..... 8G473,y = 1 .06x - 8



                                            O    ..... 86474,Y = 0.9x + 71



                                              I                 >
                                                                                            = 0.997



                                                                                            - 0.994
                                             1000
1500
2000
                                                         LV. FILTER CONCENTRATION,
                                          Figure  16.  Dynamic calibration result with particle generator.

-------
     Before  the  experiment, the cut-off characteristics of each
stage of the Andersen sampler were tested  using 0.5 to 16 ym
oleic acid particles generated by a vibrating  orifice monodis-
perse generator  and the concentration was  measured using a piezo-
balance portable aerosol monitor.  Figure  18  shows that experi-
mental results agree well with the designed penetration charac-
teristics.

     Figure  19 shows mass concentration measurements made both
by the automatic piezobalance/Andersen sampler system and by
weighing the loaded filter from each stage of  an Andersen sampler
after one week of sampling.  We did not find  evidence of a bi-
modal size distribution in this experiment, but we did obtain
similar results  using the Andersen sample  and  the automatic
piezobalance system.

     The ratio of coarse to fine particles is  shown in Figure 20
for a three-day  period.  This ratio can be very easily measured  in
real time by the combination of the modified  Andersen sampler
and automatic piezobalance.
        AMBIENT AIR
           VACUUM
           PUMP
                                   \
                                                 AUTOMATIC
                                                 PIEZOBALANCE
                                                 AUTOMATIC
                                                 PIEZOBALANCE
                                                 AUTOMATIC
                                                 PIEZOBALANCE
                                                 AUTOMATIC
                                                 PIEZOBALANCE
                            ANDERSEN AIR
                            SAMPLER
AUTOMATIC
PIEZOBALANCE
         Figure 17.  Experimental set-up for measuring the real-time sized particle
                  mass concentration.
                                237

-------
SUMMARY

     Field  testing data for measuring the mass concentration
of airborne particles and a newly-developed application of the
automatic piezobalance have been  described.  A summary of the
results  is  as  follows:

     1)  The automatic piezobalance can measure one-hour values
         of mass concentration  within ± 20%, as compared with
         LV measurements.

     2)  The automatic piezobalance can operate for  over one
         week  without maintenance.
          100
           50 ' ~
       cc

       HI
             0.1
0.5     1             5
   PARTICLE DIAMETER, )um
                                                      10
          Figure 18.  Penetration efficiency characteristics of Andersen air sampler.
                                 238

-------
    3)   A newly developed  isokinetic total and  respirable sampler
        is useful for making  dynamic calibrations  under field
        conditions and  also for minimizing wind effects and
        wall losses of  particles in sampling  tubes.

    4)   The real-time measurement of mass concentration by size,
        in the 0.5 to 20 vim range,  can be easily made using
        a modified Andersen ambient air sampler  and  an automatic
        piezobalance.
CO

 a.
 z"
 o

 <
O
o
CO
co
    20
10
                        P'
                        I
                    -~H
                           i
                                     I
                                     I	
                                                 PIEZOBALANCE
                                             ANDERSEN, FILTER
       0.1
                  0.4
                                   -n
1          3   5

 PARTICLE DIAMETER,
                                           10
11
             Figure 19.  Size distribution measurements of airborne particles.
                              239

-------
to
£*
o
                                                                                                  TEMPERATURE (OC)  HUMIDITY (%)
       DC

       O!
       01
       V)
       cc
       <

       8
            2.0
           1.5
           1.0
           0.5
                                                                                                     \
\d
                                            RELATIVE HUMIDITY
                                                                                          TEMPERATURE  /
                                                                           COARSE/FINE
                                                                   40  1100
                                                                                                               30  -
                                                                    20
                                                                                                               10  -
                                                                                                               0  J 0
        75
                                                                         50
                                                                         25
                  18       24
12      18      24       6       12       18      24      6
12
                                                          TIME, hr
                                    Figure 20.  Result of the real time measurements of the coarse/fine ratio
                                               by Andersen sampler and automatic Plezobalance.

-------
REFERENCES

1.   Sem, G.J., and K. Tsurubayashi.  A New Mass Sensor for Respir-
     able Dust Measurement.  Am. Ind. Hyg. Assoc. J. 36:791,
     1975.

2.   Sem, G.J., K.  Tsurubayashi, and K.  Homma.  Performance of
     the Piezoelectric Microbalance Respirable Aerosol Sensor.
     Am. Ind.  Hyg.  Assoc.  J.  38:580, 1977.

3.   Homma, K.  Calibration Method of Mass Sensitivity for Air-
     borne Particle Mass Monitor.  Japan Soc. Air Pollut., 1978.

4.   Daley, P.S.   The Use  of  Piezoelectric Crystals in the Deter-
     mination  of Particulate  Mass Concentration in Air.  Ph.D.
     Thesis, University of Florida, Gainesville, 1974.

5.   Tsurubayashi,  K., K.  Homma, et al.   On the Piezobalance
     Airborne  Dust Meter.   Japan Soc. Air Pollut., 1976.

6.   Tsurubayashi,  K., et  al.  Measurement of Airborne Particu-
     late Mass Concentration by Automatic Piezobalance Dust
     Monitor.   Japan Soc.  Air Pollut., 1977.

7.   Tsurubayashi,  K.  Measurement of Airborne Particulate Mass
     Concentration by Automatic Piezobalance.  Japan Soc. Air
     Pollut.,  1978.

8.   Pich, J.   Theory of Aerosol Filtration.  In:  Aerosol Science,
     C.N. Davies, ed.  Academic Press, London, 1966.

9.   Tsurubayashi,  K.  The Real-Time Measurement of Airborne
     Particulate Mass Concentration by Sizing.  Japan Soc. Air
     Pollut.,  1978.
                              241

-------
                             PAPER 14


      A NEW REAL-TIME ISOKINETIC DUST MASS MONITORING SYSTEM
                         JAMES C.F. WANG
                   COMBUSTION RESEARCH DIVISION
                  SANDIA LABORATORIES, LIVERMORE
ABSTRACT
     A new real-time dust mass monitor is being developed by
combining an automatic isokinetic sampling probe with a tapered-
element oscillating microbalance (TEOM).  Particulates from a
stack are sampled on line through the isokinetic sampler and
collected on an astroquartz mat filter of the TEOM detector.
The filter is originally excited and oscillated at a low fre-
quency (about 200 Hz).  As the particulates deposit on the fil-
ter, the mass increase of the filter is reflected in a frequency
reduction which is measured in real time and yields directly
the collected particulate mass.  The TEOM detector normally has
a high mass resolution (10~9 g) and wide dynamic range (10s - 106).
It has been desensitized for high particulate loading applica-
tions.  The integrated monitoring system was tested in a room-
temperature wind-tunnel flow with externally injected particulates.
Good agreement was obtained between the mass collected through
the isokinetic sampling system and the weight loss of the dust
feeder in real time.

INTRODUCTION

     Particulate emission control is one of the most challenging
tasks in the development of advanced fossil-fuel combustion sys-
tems.  Size distribution, dust loading density, and other critical
physical and chemical properties of particulates in the effluents
of combustors and their associated cleanup equipment comprise
the key information needed for this development.1 However, there
has been a lack of accurate and real-time particulate diagnostic
techniques for the effluents from advanced power systems.  This
has prevented efficient evaluations of the performance of com-
bustors and cleanup equipment and has made it difficult to de-
velop components in the advanced power systems to meet environ-
mental regulations and gas turbine product specifications.  There
is thus an urgent need for appropriate particulate diagnostic
                               242

-------
instruments, especially those with capabilities of nonintrusive,
in-situ, and real-time monitoring.  The difficulties which chal-
lenge the instrument designers originate from the hostile en-
vironment of most advanced fossil-fuel combustion systems.

     Conventional techniques used in industry and utility com-
panies to characterize the effluents from their boilers or fur-
naces require sample withdrawal by a physical probe with sub-
sequent dilution and/or cooling.  Insertion of the probe into
the flow may have significant effects on the flow field in the
vicinity of the probe.2  Dilution and/or cooling of the sample
during extraction may induce substantial particle size change
in the sample due to agglomeration and condensation of gaseous
species.  Furthermore, analysis of the particulates collected
is usually performed off-line and may be biased or dubious be-
cause of difficulties associated with redispersion of the par-
ticulates in the analyzer.

     The physical sampling method is, however, the only means
of providing samples of particulates for detailed analyses of
their physical and chemical properties.  The lack of reliable
and unbiased physical sampling probes for high-temperature, high-
pressure fossil-fuel combustion environments causes uncertainties
in evaluation and modification of the combustors and cleanup
equipment.  An automatic, relatively nonintrusive sampling system
is being developed at Sandia Laboratories as the first step
toward the development of a reliable and unbiased physical sampl-
ing system.  An on-line mass detector is also being developed
to couple with the isokinetic probe to obtain real-time dust
loading measurements.

ISOKINETIC SAMPLING SYSTEM

     The process of physically extracting a sample from a flow
system inherently disturbs the properties being measured.  One
of the major sources of error in sampling is the discrimination
error of particle size due to the probe intrusion in the sampled
flow  (aerodynamic error).  If the sampling velocity is greater
than the undisturbed flow velocity due to heavy suction, smaller
particles are extracted preferentially since they follow the
gas stream lines more readily.  On the other hand, if the flow
must decelerate on entering the probe, the larger particles
continue moving into the probe as a result of their inertia,
thus increasing their concentration.  If the sampling velocity
is matched to the free-stream velocity, i.e., isokinetic sampl-
ing, the size distribution and mass loading density in the sampled
stream are preserved.

     The magnitude of sampling errors from anisokinetic sampling
has demonstrated the necessity of well-characterized sampling
conditions, especially for particles in the range of 0.5 to 100 urn
in diameter.3   In practice there can be uncertainty in obtaining
                               243

-------
true isokinetic sampling conditions.  A common method of iso-
kinetic sampling involves measuring and matching volumetric flow
rates of the probe and the free stream.  This necessitates mea-
surements of pressure and temperature at the probe inlet.  For
fossil-fuel combustor exhaust flows, where velocity, temperature,
and pressure fluctuate, it becomes difficult to follow these
variations and maintain the isokinetic sampling condition.  A
second method is to match the static pressures at the probe inlet
and in the free stream. "*  The isokinetic sampling condition can
easily be achieved by nulling the difference between the two
static pressures via a throttling valve which controls the sampl-
ing flow rate.  An automatic isokinetic sampling system has been
developed employing an electromagnetic control valve based on
the "null" principle.5  However, an automatic backflush mechanism
should then be built into the sampling system to prevent the
static pressure sensors from becoming plugged in the high dust
loading environments commonly encountered in advanced power
systems.6

     The automatic sampling system developed at Sandia Labora-
tories consists of (1) a sampling probe,  (2) two static pressure
sensors,  (3) an isokinetic sampling controller,  (4) a throttling
control valve, and (5) a flow meter.  Figure 1 shows the schematic
of the sampling system.  The sampling probe is made of 6.35-mm
O.D. and 4.45-mm I.D. stainless steel tubing and is shown sche-
matically in Figure 2.  The sampled-flow static pressure tap
holes are located in the sampling nozzle wall at about six nozzle
diameters downstream from the nozzle tip.  The free-stream static
pressure sensors are on a 3.175-iran O.D. stainless steel tube
placed above and parallel to the sampling nozzle.  This sampling
nozzle and sensors configuration was demonstrated successfully
in pressurized fluidized bed exhaust environments.7  The two
static sensors are connected to each side of the Validyne dif-
ferential pressure transducer via 3.175-mm O.D. stainless tubes.
The pressure transducer is protected by shunt tubing via a
solenoid valve which is open during the backflush process.  The
shunt is also used to zero the pressure transducer before each
sampling operation.

     The isokinetic sampling controller is presently simulated
by using a PDPll-34 minicomputer.  A hardwired electronic con-
troller will be built after the system response  from each com-
ponent is identified.  As shown in Figure 1, the output  from
the Validyne differential pressure transducer is measured on
a Validyne Model-CD12  indicator.  The output from the indicator
is then input to the minicomputer through an A/D converter.
The computer sends a control signal to the electromagnetic
throttling control valve to increase or decrease the sampling
flow depending on the  input from the indicator.  A  zero  input
from the  indicator corresponds  to the  isokinetic sampling condi-
tion; thus no action  is applied to  the throttling valve.
                               244

-------
to
*>
Ul
                                        1SAMPLING
                                    \\lfir PROBE
                   cswooo yZZZZZZs,
                                                                •FLOW
                                                                           NEEDLE
                                                                            VALVE
                                                                                                  BACKFLUSH
                                                                                                   AIR INLET
                                               SAMPLING
                                            STREAM SENSOR




1
OPEN

DEL

CLOS

CLO
SHU

                                               Figure 1. Automatic isokinetic sampling system.

-------
     The static pressure  sensors are periodically backflushed
with dry nitrogen  to  prevent  blockage of the tap holes.  During
the backflush, the gas  flow in the sensing line may produce  an
erroneous signal to the pressure transducer.  Consequently,
during this period, the automatic control is interrupted by  an
electronic "sample and  hold"  circuit.  This circuit continuously
holds the signal from the controller to the throttling valve,
          FREE STREAM STATIC
            PRESSURE SENSOR
      MEAN
      FLOW
    DIRECTION
              SAMPLING
                NOZZLE
           NOZZLE INLET STATIC
             PRESSURE SENSOR
                                       SAMPLED
                                          GAS
                                            TO PRESSURE
                                           TRANSDUCERS
                Figure 2. Schematic of the isokinetic sampling probe.
                                246

-------
which is held, until the backflush is completed, at a value cor-
responding to the isokinetic flow just prior to the backflush.
The periodic backflush sequence can be overridden by the operator
at any time.  This allows a continuous backflush mode of opera-
tion for very high dust loading environments.  When the system
is operated in this mode, the backflush flow must be reduced
to levels which do not produce erroneous signals in the static
pressure sensors.

     The automatic isokinetic sampling system is also designed
to permit manual operation.  For a specific sampling nozzle inlet
cross-section, the mass flow corresponding to isokinetic condi-
tion can be computed from the measured pressure, temperature,
and velocity of the sampled flow.  The sampled gas flow can then
be manually adjusted via the throttling valve to match the com-
puted isokinetic mass flow.  This manual operation provides an
independent backup system for automatic operation.

REAL-TIME MASS DETECTOR

     A patented real-time mass measurement—a device tapered-
element oscillating microbalance8 (TEOM)—is being adapted for
ambient air particulate loading density monitoring.  In this
work, the TEOM has been modified to provide real-time dust load-
ing measurements for exhausts from fossil fuel combustors.

     The active element of the TEOM consists of a tube constructed
with high mechanical quality factor and having a special taper
(Figure 3).  This tube is firmly mounted at the wide end; the
other end supports an exchangeable filter which can be fabricated
from virtually any material.  The tapered tube with the filter
at the free (narrow) end is set into oscillation in a clamped-
free mode between two electrostatically charged parallel-field
plates.  Dust-laden air is drawn through the filter and the hol-
low tapered tube via a vacuum pump.  A feedback system maintains
the oscillation, whose natural frequency will change in relation
to the mass deposited on the filter.  The sensitivity and fre-
quency can be chosen at will by proper dimensioning of the oscil-
lating tapered element.

     Simplified operational details are shown in Figure 3.  The
tapered element is originally excited into oscillation and kept
in oscillation at its natural frequency by a feedback system
which consists of a light-emitting diode photo-transistor com-
bination.  The oscillation of the tapered element is converted
into an electrical signal from the diode photo-transistor set
via the light-blocking effect of the oscillating element.  The
amplified signal from the photo transistor is fed back to the
conducting surface of the tapered element.  The electrostatic
charges on the tapered element are then modulated by this feed-
back signal and interact with the electrostatic field between
                               247

-------
                  SIDE VIEW
                          TOP VIEW
                                FILTER
to
>£>•
00
                   TO PUMP
                                     TAPERED ELEMENT
                                            FIELD PLATES
 CONDUCTIVE
PATH TO FIBER
                                                                                    LED
                                                                                    PHOTO TRANSISTOR
                                                                                     DATA
                                                                                   PROCESSING
                                      Figure 3. Schematic of the TEOM system.

-------
the two parallel field plates, so that a steady-state  oscilla-
tion of the tapered element at its natural  frequency  is  estab-
lished.  This frequency will change as the  weight of  the filter
increases because of the particulate deposition.  A photograph
of the detector assembly and the electronic controller  is  shown
in Figure 4.

     The TEOM is an oscillator whose frequency can be  described
with two parameters, the restoring force constant K and  the  ef-
fective mass m, consisting of the mass of the filter,  rop,  the
effective mass of the tapered elastic element, mo, and  the filter
loading, Am:

               m = mp + mQ + Am.                               (1)

The relation between these quantities is given by the  expression

               4lT2f2 = K
                       m                                       ^ '

or



               f2 = ST  with Ko = ^1 •                        (3)

     If the TEOM is initially oscillating at a frequency fa  cor-
responding to mass m and exhibits a frequency fj-, after a mass
uptake, the change in mass Am can be obtained as a function  of
fa, fb, and Ko; namely,
and

                      K

               fb = in  + Am '
                     3.

Elimination of ma by combining Equations 4 and  5 leads  to

               Am = KQ  (l/f£ - l/fa).                          (6)

Note that Equation 6 is independent of the filter mass  mp and
the effective mass m  of the oscillating tapered element.  Equa-
tion 6 is also used for calibration by measuring Am gravimetri-
cally, thus obtaining KQ.

     In reality the frequency is not measured directly.  Instead,
one measures the time interval T required for completing a cer-
tain number of cycles, N, of the TEOM's vibration.  During this
                               249

-------
Figure 4.  TEOM detector and its controller.

-------
gated time interval, T, a high-frequency clock  (running at a
frequency f_) registers a number of counts C.  This procedure
leads to measurement of the time interval with great accuracy
(5 to 6 significant figures).  Since


               Ti = fy    (i = a or b)                          (7)
and
               C. = T.f     (i = a or b)                        (8)
                I    .L C
Equation 6 becomes



               Am = iFF    '
                       c

Thus the mass uptake Am is determined by Ko  (a property of  the
tapered elastic element), the chosen circuit parameters N and
fc, and the counts Ca and C]-, measured before and after the  mass
uptake, respectively.

     Unlike most other microbalances, the TEOM is mechanically
strong and is easily automated with data output consisting  of
frequency information in  the 10 to  102 Hz range.  Mass deposi-
tion is monitored in real time.  A  dynamic operating  range  of
over six orders of magnitude., from  micrograms to grams, is  achieved,

     Although the TEOM measures mass by a frequency shift,  as
does a QCM  (quartz crystal microbalance), there is no further
similarity.  Particulate  collection on a QCM can only be achieved
by impaction on the crystal surface.  Particulate collection
in this version of the TEOM is through a filter whose mass  is
continuously monitored by the vibration of the hollow, tapered,
elastic element.

     A QCM has nonuniform mass sensitivity across its surface,
and its high oscillation frequency  (10 MHz)  produces  a high sur-
face acceleration.  This necessitates strong adhesive forces
for the particles; however, even if the adhesive forces are
strong enough to prevent particulates from breaking loose under
the surface acceleration, any mass above the immediate contact
surface will fall out of phase with the crystal oscillation,
leading to the well-known saturation effect of QCM's.  After
a buildup of a few microns in thickness, any additional mass
deposition is no longer reflected in a frequency decrease,  thus
restricting QCM's to a low upper limit in measurable  total mass
deposition.  QCM's can neither measure particulate depositions
over a thickness of a few microns nor can they measure the mass
of particles exceeding a few microns in size.  Consequently,
they are totally unsuitable for measuring high concentrations
of relatively large particles such as are found in smokestacks.


                               251

-------
     The TEOM has none of these problems.  All particles of in-
terest are trapped in the filter and result in a frequency shift
which is limited only by the capacity of the filter itself.

ROOM TEMPERATURE WIND TUNNEL

     The integrated isokinetic real-time dust mass monitoring
system was tested in a room temperature wind tunnel flow with
externally injected particulates.  A schematic of the wind tunnel
facility is shown in Figure 5.  The driver is a 5-hp low head
air blower which is used in the suction mode.  The air inlet
is a 25.4-cm diameter opening through the building wall.  A con-
traction cone reduces the air passage to a 10-cm diameter down-
stream from a section of honeycomb flow straightener.  A T-section
with a particulate injector mounted on the side flange is con-
nected at the exit of the contraction cone.  A second T-section
with the isokinetic sampling probe and sensors mounted on the
side flange is installed downstream from a 1.2-m-long straight
Pyrex-glass pipe section after the first T-section.  This straight
pipe allows the injected particulates to mix with the air flow
and develop into a more uniform distribution of particulates
across the sampling cross section.  The air flow after the sampl-
ing section is then turned 180° and exits to the inlet of the
air blower.  The flow rate through the wind tunnel can be ad-
justed between 50 and 450 SCFM via a manual butterfly valve at
the exit of the blower.  Downstream from the butterfly valve,
at about 15 exhaust pipe diameters, a pitot-static pressure type
flow meter is installed to measure the actual flow rate.

     A cyclone type particulate feeder was designed, fabricated,
and tested to provide continuous and uniform injection of fly
ash into the wind tunnel for particulate diagnostic tests.  The
fly-ash feed rate can be controlled via the pressure drop across
the feeder bed, and monitored on-line in real time via an elec-
tronic balance.  Figure 6 shows a typical dust-feed history in
terms of the weight loss of the feeder.  The nearly straight
line in Figure 6 demonstrates the uniformity of the dust feed
rate.  The dust loading density in the test section of the wind
tunnel can be varied between 0.01 and 10 g/m3 using this feeder
assembly.  Because of the naturally generated electrostatic
charges from the fluidized fly-ash particulates inside the feeder,
electrical grounding of the feeder was found necessary for optimum
performance and safety.

     The fly ash used  in the wind-tunnel tests was obtained  from
cyclone catches at the exhaust cleanup system of Exxon's mini-
plant pressurized, fluidized-bed  facility.  Fly ash obtained
from two cyclone catches in series was roughly preclassified
at mean diameters of 1 and 5 urn,  respectively.  Prior to being
loaded into the particulate feeder, the  fly ash was  sieved at
200 mesh to break up agglomerated particles and remove large
particles.  A typical  size distribution  of the fly ash from  a
Coulter analyzer is shown  in Figure 7.
                               252

-------
U1
U>
                                   ISOKINETIC
                                   SAMPLING PROBE
PARTICULATE
INJECTOR
                                                                 MECHANICAL BALANCE
                                     Figure 5. Schematic of the room temperature wind tunnel.

-------
PRELIMINARY EXPERIMENTAL  RESULTS

     The automatic  isokinetic  sampling system was tested in the
room temperature wind  tunnel described above.  The sampling flow
was established via  a  vacuum pump and measured by a Hasting mass
flow meter.  A positive filter  using an astroquartz mat was used
to collect the particulates from the sampling nozzle.  The free
stream velocity was  measured by a pitot-static flow meter at
the exhaust of the wind-tunnel  blower.  Using the signal from
the differential pressure transducer, the PDPll-34 minicomputer
automatically adjusted the throttling control valve on the sampl-
ing line.  Isokinetic  sampling  condition was achieved automati-
cally  (when the differential static pressure was nulled) less
than a second after  the free stream flow rate was changed.  The
response of the sampling  system was designed to be about 10 Hz,
which  is adequate for  most applications in the combustor exhausts
of advanced power systems.
      1.5
   CO
   CO
   O
   X
   <3
   LLJ
   DC
   O

   O
      1.0
      0.5
        0
100
200
300
400
500
                              TIME, sec
                  Figure 6. A typical history of dust feed rate.
                               254

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x
a
100


 90


 80


 70


 60


 50


 40


 30


 20-


 10-
      0
      I    I
0   0.15 0.2
                                                             S-
CUMULATIVE DISTRIBUTION
                        I  I  I I
                       0.3 0.40.5
                           PARTICLE SIZE
                           DISTRIBUTION
1.0        2

     PARTICLE DIAMETER,
             1
             15   20    30  40  50
                                                                                                   100
                                         Figure 7.  Size distribution of fly ash.

-------
     Figure 8 shows the experimental results of  a comparison
of the measured sampling velocity and  the  free stream velocity
at the zero differential pressure condition maintained  by  the
computer.  The close agreement between the two velocities  demon-
strates achievement of true  isokinetic sampling  conditions with
the present sampling configuration with an estimated overall
accuracy of better than 5%.

     The amount of particulate matter  collected  at the  astro-
quartz filter element was found to be  generally  less than  ex-
pected for isokinetic sampling at uniform dust loading  across
the test section.   Several factors contributed to this  discre-
pancy.  A portion of the particulates  was collected on  the inside
wall of the sampling probe.  Clear evidence was  also found via
light scattering techniques that the radial dust loading density
distribution at the inlet of the sampling probe  was not uniform
and, in fact, varied as a function of  the wind-tunnel flow rate.
Figure 9 shows a typical comparison of the weight of collected
samples relative to what is expected from a uniform dust distri-
bution in a free stream at isokinetic  sampling conditions.  At
each flow rate, the weight ratio was nearly constant and repro-
ducible.   This ratio was observed to depend upon the electro-
statics of the injected fly-ash particles and the potential of
the sampling probe.  Best results appear to occur when  the sampl-
ing probe is grounded.  However, the influence of electrostatic
charging on dust collection needs further detailed study to
optimize the isokinetic sampling processes.  On  the other  hand,
the size distribution of collected fly-ash particles appeared
to be similar to that shown in Figure  7.

     A preliminary test of the TEOM detector coupled to the iso-
kinetic sampling system was performed  in the room temperature
wind tunnel.  The history of the collected particulates was re-
corded in real time.  At the end of each sampling test, the filter
element of the TEOM detector was weighed and compared to the
accumulated frequency shift displayed  on the recorder.  Figure 10
shows the good agreement obtained between the real-time measure-
ments and the accumulated weights in typical calibration tests.
A calibration constant of 4.62 x 10~3  g/Hz was found from  a least-
squares fit of the calibration data.

     In Figures 11(a)  and  (b) are shown, respectively,  photo-
graphs of the TEOM filter prior to being mounted on the TEOM's
tapered element and after it had collected about 16 mg  fly ash.
Most of the fly ash collected was near the top of the astroquartz
mat as shown in Figure 11(c).  Figure  11(d) shows the back side
of the same mat shown in Figure 11(c)  and demonstrates  that there
was no trace of fly ash penetration through the  astroquartz mat.
The properties of light weight, ease of handling, and 100% col-
lection efficiency for particles 1 um  and larger make the  astro-
quartz mat an ideal filter material for the TEOM application.
Furthermore, the astroquartz mat was tested at elevated tempera-
ture environments and proven to be useful up to  800°C.
                               256

-------
        Experiments on real-time dust-loading monitoring  were  per-
   formed  using  the combined system of the isokinetic  sampling probe
   and  the TEOM  detector.   The weight loss of the dust feeder  was
   also monitored in real  time with the combination of a  mechanical
   balance and electronic  scales (see Figure 1).  A typical test
   result  is  shown in Figure 12.  Output from the TEOM detector
   was  scaled up to the total flow in the test  section on the  basis
   of the  ratio  of the sampled flow to the total flow  and the  empiri-
   cal  dust distribution at the inlet of the sampling  probe.   Thus,
   direct  comparison of the dust collected to the weight  loss  of
   the  dust feeder as a function of time could  be obtained.  Close
   agreement  is  shown in Figure 12 between the  dust collected  on
   TEOM and that injected  into the wind tunnel.  As indicated, the
   dust feed  rate was changed twice.  The TEOM  output  essentially
   matches the dust feed rate and follows, with acceptable response,
   changes in the feed rate.  The real-time on-line dust  loading
   monitoring capability is demonstrated.
V,
     1.1
     1.0
     0.9
     0.8
                                                      $     $
       0
10         15         20

 FLOW VELOCITY, Vo, m/sec
25
                                                                    30
                  Figure 8. Test results of the isokinetic sampling system.
                                  257

-------
                         1.0r-
to
Cn
oo
                         0.8
                         0.6
                W,
0.4
                         0.2
                          0
                            0
                 20
40             60            80            100            120           140
                                                                           Q, I/sec
                                                              Figure 9.  Dust collection test results.

-------
                                6SZ
                   CALIBRATION CONSTANT    -, g/Hz x
                         ro
                                 CO
s
c8
     O
     o
0}
o
-*,
m

o


m

O
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    tvj

    O
                                                   NJ

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                                                   X

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-------
                                            Sandra laboratories
  (a)
                                                 (b)
                                         Sandia laboratories
(c)
                                             (d)
                Figure 11.  TEOM filters.

-------
                                   T93
                       ACCUMULATED DUST FEEDER WEIGHT LOSS, g
                            N)
                                  CO
a1
«•»

I
3
.a
s
Ql
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I


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 5'
O

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-------
SUMMARY

     The combination of an automatic isokinetic sampling system
and the TEOM real-time mass detector has been demonstrated to
be a promising real-time particulate mass monitoring system for
high dust loading environments.  The bench test model described
in this paper was designed for near room temperature and one
atmospheric pressure condition.  Additional development is under-
way to extend this new monitoring system to high temperature
and high pressure applications.  Automatic self-cleaning features
and/or interchangeability for the TEOM filter during sampling
processes are planned to be developed for continuous particulate
mass loading monitoring applications.  A particularly useful
development which we are exploring is the incorporation of a
TEOM detector at each dust collector of a cascade cyclone train.
Such a system will permit real-time analyses of mass loading
distribution according to particle size.

ACKNOWLEDGEMENTS

     The author would like to thank J. Teodoro and T. Schoeppe
for their help in building the test facility and performing the
experiments.  This work is sponsored by the Heat Engines Branch,
Office of Fossil Energy, U.S. Department of Energy and is a part
of the Sandia Laboratories' Diagnostic Assessment for Advanced
Power Systems Program.


REFERENCES

1.   Coleman, H.W., D.R. Hardesty, R.J. Cattolica, J.H. Pohl,
     L.A. Rahn, R.A. Hill, and D.L. Hartley.  Diagnostics Assess-
     ment for Advanced Power Systems.  Sandia Laboratories Report
     SAND79-8216, 1977.

2.   Vitols, V.  Theoretical Limits of Errors Due to Anisokinetic
     Sampling of Particulate Matter.  J. Air Pollut. Control
     16:79, 1966.

3.   Performance and Measurements at Dust Collectors.  Verein
     Deutscher Ingenieure, VDI-2066 Standards, 1966.

4.   Branch, M.C.  Sampling From High Temperature Particle Laden
     Flows.  Sandia Laboratories Report SAND78-8253, 1978.

5.   Ringwall, C.G.  Compact Sampling System for Collection of
     Particulates from Stationary Sources.  EPA-650/2-74-029,
     U.S. Environmental Protection Agency, Research Triangle
     Park, NC. 1974.
                               262

-------
6.   Wang, J.C.F., C.G.  Ringwall, and C.M. Thoennes.  A High-
     Temperature,  High-Pressure Isokinetic/Isothermal Sampling
     System for Pressurized Fluidized Bed Application.  In: Pro-
     ceedings 5th International Conference on Fluidized Bed Com-
     bustion, Washington,  DC,  Vol III, p. 326, 1978.

7.   Wand, J.C.F., R.R.  Boericke, and R.A. Fuller.  A High-Tempera-
     ture, High-Pressure,  Isokinetic/Isothermal Sampling System
     for Fossil Fuel Combustion Applications.  In:  Proceedings,
     Symposium on Transfer and Utilization of Particulate Control
     Technology.  EPA-600/7-79-044d, U.S. Environmental Protec-
     tion Agency,  Research Triangle Park, NC, 1979.  p. 310

8.   Patashnick, H.  U.S.  Patent 3,926,271, December,  1975.
                              263

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                             PAPER 15


   A NEW REAL-TIME AEROSOL MASS MONITORING  INSTRUMENT:   THE  TEOM
                         HARVEY  PATASHNICK
                         GEORG  RUPPRECHT
                 RUPPRECHT AND PATASHNICK COMPANY
ABSTRACT
     A real-time monitoring device for airborne particulate matter
has been developed on the basis of a novel mass measuring device.
This new patented instrument is called a TEOM, Tapered Element
Oscillating Microbalance (Am/m < 10~6, dynamic range > 106).
Two aerosol monitoring techniques are utilized with this instru-
ment, an impaction device  (mass resolution 3 x 10~10 g) and a
filter device (mass resolution 5 x 10~8 g).  The TEOM filter
unit uses exchangeable filter cartridges.  Time resolution is
1 minute for the impactor TEOM and 30 minutes for the filter
TEOM.  (Time resolution:  time required to measure an air pollu-
tion level of 10 yg/m3 with an accuracy of 10%.)  The impactor
TEOM is used to measure the particulate content of air with high
time resolution, while the filter TEOM provides an absolute mea-
surement.  The filter TEOM effectively represents a real-time
absolute standard for the measurement of particulate mass con-
centration in the air.

DESCRIPTION OF THE TAPERED ELEMENT OSCILLATING MICROBALANCE,
TEOM

     It cannot be over-emphasized that the TEOM is significantly
different from gravimetric and quartz crystal microbalances
(QCM's).  The active element of a TEOM consists of a tube con-
structed of a material with high mechanical quality factor and
having a special taper.  This tube is firmly mounted at the wide
end while the other end supports a substrate  (or filter cartridge)
which can be composed of virtually any material.  The tapered
tube with the substrate at the free  (narrow) end is set into
oscillation in a clamped-free mode.  A feedback system maintains
the oscillation whose natural frequency will change in relation
to the mass deposited on the substrate (or filter).  The sensi-
tivity and frequency can be chosen at will by proper dimensioning
of the oscillating tapered element.
                               264

-------
     The operation of a TEOM is shown in simplified manner in
Figure 1.  The tapered element is kept in oscillation by a feed-
back system.  The oscillation of the element is converted into
an electrical signal by a light-emitting diode-phototransistor
combination, the output of the phototransistor being modulated
by the light-blocking effect of the vibrating element.

     Unlike most other microbalances, the TEOM is mechanically
strong and is easily automated with data output consisting of
frequency information in the 102 to 103 Hz region.  Mass deposi-
tion is monitored on a real-time basis.

     A photograph of a typical instrument is shown in Figure 2.
The unit illustrated here has a dynamic operating range over
six orders of magnitude from 10~8 g to tens of milligrams.  This
is a nominal sensitivity range; greater or less sensitivity can
be achieved by adjusting the dimensions of the oscillating ele-
ment and the substrate.

AEROSOL MONITORING OPTIONS WITH THE TEOM

     The TEOM can be used to measure aerosol mass concentrations
with two different particulate collection techniques, impact ion
and filtration.  These two methods are illustrated in Figure 3.
Figure 3a shows the  impaction method where particulates in the
air stream are impacted against a substrate  (greased or ungreased)
on the TEOM.  Typical mass sensitivity for an impactor TEOM is
in the order of 3 x  10"10 g.  Classical impaction techniques,
however, have well known difficulties and as a result, a filtra-
tion TEOM unit has also been developed.  The filter unit was
developed to represent an absolute standard for the real-time
measurements of aerosol mass concentrations.  In this configura-
tion, shown in Figure 3b, a filter cartridge is placed at the
free  (narrow) end of the hollow tapered element.  Particulate-
laden air is drawn through the filter, and the resulting filtered
air is pumped down the hollow tube.  Photographs of a TEOM filter
unit are shown in Figure 4.

THEORY OF OPERATION

     The TEOM is an  oscillator whose frequency can be described
with two parameters, the restoring force constant, K, and the
effective mass, m, consisting of the mass of the filter  (or sub-
strate) , mF, the effective mass of the tapered elastic element,
m0, and  the filter  (or substrate) loading, Am.

               m = HL, + m  + Am                                (1)
                     r    O

The relation between these quantities  is given by the expression:


               4TT2f2 =                                         (2)
                               265

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     SIDE VIEW
TOP VIEW
                           SUBSTRATE


                            FIELD PLATES
                          TAPERED
                          ELEMENT


                          ,_ CONDUCTIVE
                             PATH TO FIBER
             LED
                                                                   PHOTO TRANSISTOR
  77/7'/////////
L_
i
AMP

u
L

COUNTER



1


DATA
PROCESSING
Figure 1.    Tapered element oscillating microbalance (TEOM) configuration (typical).
                   TEOM OPERATION

                   1. Electric field is set up between field plates.
                   2. Image of tapered element is projected on phototransistor.
                   3. Oscillation of element initiated electrically or mechanically
                      produces an AC voltage output from phototransistor.
                   4. AC voltage is amplified and applied to conductive path on
                      element which maintains the oscillation due to interaction
                      with field set up in Step 1.
                   5. Frequency of oscillation, and hence mass on substrate, is
                      determined by frequency counter.
                                          266

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Figure 2. Typical TEOM; substrate disc is at top center.
                       267

-------
or
f2 = sr  with Ko
                                                                   (3)
CALIBRATION PROCESS



      If  the mass Am  is  determined  gravimetrically  and added  to

the filter, Ko can be determined from the frequencies fj and

f2 where fj is the frequency without  Am and f2  is  the frequency

with  the filter loading mass Am.   It  is
                        K
                 :2 _
                     mF + mo
                                                                   (4)
                          K
                 2 _

                   ~
                     nu, + m  + Am
                       r     O
                                                                   (5)
            AIR FLOW
                   NOZZLE
                   SUBSTRATE
                                             AIR FLOW
                                                       FILTER
        TEOM IMPACTION UNIT
                          TEOM FILTER UNIT
               3a
                                3b
             Figure 3. Aerosol monitoring options with the TEOM.
                                 268

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  AIR INLET
 ELECTRICAL
 CONNECTOR
life,*, •
                                                    FILTER

                                                 FEEDBACK
                                                 ELECTRONICS
                              Figure 4.  TEOM filter unit.

-------
From these two equations K0 for a particular device can be cal-
culated:
                         Am
                                                               (6)
MASS MEASUREMENTS

     If the TEOM is oscillating to start with at the frequency
of fa and exhibits the frequency ft, after a mass uptake,  Am  can
be obtained as a function of fa, fj-, and Ko.  It is
                    K
               f2 = -2
                a   m
                      K
               fz = 	0_
                b   m + Am
Elimination of m leads to
               Am = KQ  (1/f* - 1/f2)
                                 (7)
                                 (8)
                                 (9)
As is evident in Equation 9 the relation between frequency and
mass uptake is not linear.  Note that Equation 9 is  independent
of the filter mass, mp, and the effective mass, mo,  of  the oscil
lating tapered element.
     For relatively small frequency changes
                Af_
                f
«1
(10)
Equation 9 can be linearized, but this will only be  an  approxi-
mation.

     In reality the frequency is not measured directly.   Instead,
the time period, T, required for completing a certain number,
N, of cycles of the TEOM's vibration is measured.  During this
gated time period, T, a high frequency clock  (running at  a fre-
quency  fc) registers a number of counts, C.  This procedure
leads to measuring the time period with great accuracy  (5 to
6 significant figures).  Since
                    N
                               (i  = a or b)
                                (11)
and
               Ci = Vc
(i = a or b)
(12)
                               270

-------
Equation  9  becomes
                      K
                Am  = -7^7  
-------
(QCM's have oscillation  frequencies in the megahertz region,
whereas the TEOM  oscillates around 100 Hz.  Surface acceleration
is proportional to  f2.)   Also the TEOM is uniformly sensitive
to mass across the  entire substrate surface.  This eliminates
the need for a small  sample site, rendering the total substrate
surface area available for  particle capture which, combined with
a low surface acceleration, drastically reduces saturation ef-
fects.  Additionally, even  masses of particles hundreds of microns
in size can be measured.   The TEOM, although highly sensitive,
has a sufficiently  large  dynamic range, due to its low suscepti-
bility to saturation, to  allow sampling for long periods of time.
Furthermore, virtually any  type of substrate can be used  (filters,
low Z materials,  reactive surfaces, etc.).

AEROSOL MASS MEASUREMENTS WITH THE TEOM

     Typical results  of measurements with the filter TEOM unit
are shown in Figure 5 which exhibits aerosol mass concentration
as a function of  time over  one day.  Data were taken in real
     30
 co

 i
 o
 o
 O
 o
 111
     20
     10
         I   I  I   1  I   I  I   I  I   I   I  I   I  I   I  i   I  I   I   I
          0600     0900     1200     1500     1800     2100    2400

                                 TIME, hr


            Figure 5. Air pollution in Albany on 12/11/78 (residential area) with
                   the TEOM filter unit.
                                272

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time every  15 minutes  with a flow rate of 5 H/min through a mem-
brane filter cartridge with a 1 ym pore size.  To eliminate the
effects of  humidity, a hydrophobic filter (Teflon) was used and
the air stream  and  the instrument were maintained at 50°C.  This
particular  unit  had  a mass resolution of 6.5 x 10
                                                  - 8
The varia-
tion of  the  aerosol  level during the course of the day  is,  to
a great  extent,  related to the traffic pattern.

     Aerosol measurement  results with a TEOM impaction unit are
shown in Figure  6.   A  single  stage impactor with a 50% cutpoint
at 0.5 ym was used.  The  impaction substrate was made of titanium
(ungreased) with a resulting  collection efficiency of 10% cali-
brated against the filter  unit as a standard utilizing the ambient
aerosol.  This efficiency will vary somewhat if there are signi-
ficant changes in the  aerosol size distribution compared to the
ambient distribution it was calibrated against, but the purpose
of using an ungreased  substrate surface was to enable the instru-
ment to operate  unattended for weeks without maintenance (greased
surfaces would eventually saturate).  The flow rate was 3 H/min
       0900
                                                           2100
          Figure 6. Air pollution on 12/14/78 versus wind condition measured
                 with the TEOM impaction unit.
                               273

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and data  were  taken during 3-minute  sampling periods.  The  mass
resolution  was 3 x 10 10 g.  As with the filter unit, this  instru-
ment was  also  run at 50°C to eliminate humidity effects.  The
results shown  in Figure 6 depict  an  initially low pollution level
(due to snowfall and high winds),  which increased significantly
as the wind direction changed and  the wind speed decreased.

     Results from both units as they were run side by side  are
shown in  Figure 7.  It can be seen that, with the exception of
one peak  near  23:10, the measurements showing aerosol variations
correlate well.  The peaks and valleys evident with the  impactor
unit are  somewhat sharper due to  the higher time resolution capa-
bility of that instrument.
                —i—i—i  i—i—I—i	1—i   i—i	1—r~—i

                O TEOM FILTER UNIT (10 MINUTE SAMPLING)
                D TEOM IMPACTION UNIT (3 MINUTE SAMPLING)
             2200
2300
2400
0100
                                  TIME, hr
         Figure 7. Simultaneous measurements with TEOM filter and impaction
                unit (12/12/78).
                                274

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CURRENT DEVELOPMENT

     The TEOM detectors are currently being mated with particle-
size separators such as the dichotomous sampler and cyclones.
A microprocessor is being employed to completely automate the
devices.  A desensitized TEOM filter unit is also being developed
with an isokinetic sampler for utilization as an on-line stack
sampling system.

SUMMARY

     The Tapered Element Oscillating Microbalance (TEOM) repre-
sents a new, unique instrument capable of real-time aerosol mass
concentration measurements utilizing two collection techniques,
impaction and filtration.  The impaction unit is capable of higher
time resolution, but the filter unit eliminates uncertainties
inherent with impaction collection techniques.  The TEOM filter
unit measures the mass of the collected particles and the mass,
only, independent of their composition, Z values, optical proper-
ties, shapes, or any other particle property.  It can be con-
sidered a detector which represents a real-time absolute standard
for the measurement of particulate mass concentration in the
air.

ACKNOWLEDGEMENT

     The authors wish to thank the Environmental Protection
Agency  for partial support of this work under grant R805222020.
                               275

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                             PAPER 16
           NEW AUTOMATED DIFFUSION BATTERY/CONDENSATION
             NUCLEUS COUNTER SUBMICRON SIZING SYSTEM:
  DESCRIPTION AND COMPARISON WITH AN ELECTRICAL AEROSOL ANALYZER
                          GILMORE J. SEM
                         JUGAL K. AGARWAL
                        CHARLES E. McMANUS
                         TSI INCORPORATED
ABSTRACT
     During the past several months, an automated system of in-
struments for measuring aerosol size distribution in the 0.005 to
0.2 ym diameter range has become commercially available.  The
system consists of (1) a multiple screen diffusion battery, (2)
a continuous flow, non-pulsing condensation nucleus counter (CNC),
and (3) a switching valve to allow the CNC to detect the concen-
tration at each battery port.  The system measures urban atmo-
spheres continuously for several days without maintenance.  It
requires about 4 min to measure one distribution.  The  sys-
tem is useful for accurate measurements in relatively dirty
atmospheres (>106/cm3) and in clean atmospheres  (
-------
available instruments.   The report also describes a computerized
data  reduction technique for  the diffusion  battery.   Finally,
the report describes results  of  several simultaneous  comparisons
between  two commercially available techniques for making real-
time  submicron aerosol  size distribution measurements:   the
multiple screen diffusion battery and the electrical  aerosol
analyzer.

DIFFUSION BATTERY  SIZING SYSTEM

      The instrumentation system  used for this study included
a multiple screen  diffusion battery, a continuous flow  condensa-
tion  nucleus counter (CNC) and a valving system to switch the
CNC inlet between  the 11 exit ports of the  diffusion  battery.
Figure  1 shows the system schematically.  This particle sizing
system  is useful for diameters from 0.005 to 0.2 ym.

      The multiple  screen diffusion battery  was first  described
by Sinclair and Hoopes2 in 1975.  The diffusion battery consists
of 55 four-cm-diameter  stainless steel screens with 250 wires
                                      CONDENSATION
                                    NUCLEUS COUNTER
                                     TSI MODEL 3020
        CYCLING, TIMING,
         AND RESET
       CONTROL CIRCUITRY
                                    OUTLET
VALVE |
MOTOR
                      i  ROTARY VALVE:
                      !  .12 PORTS IN
                      1 'I I PORT OUT
                                          0.3 L/min FOR CNC
                                             SAMPLE
                                                 EXCESS FLOW CONTROL
     I SWITCHING VALVE
       MODEL 3042
    AEROSOL IN
     4L/min
                                   PUMP
                                                     EXCESS FLOW:
                                               TO MAINTAIN 4L/min AEROSOL FLOW
                                                THROUGH DIFFUSION BATTERY
                      DIFFUSION BATTERY
                       TSI MODEL 3040
         Figure 1. Schematic diagram of the diffusion battery, switching valve, and
                condensation nucleus counter aerosol sizing system.
                                  277

-------
per cm.  Normally, 4 8,/min of aerosol is drawn through the screens
in series.  The screens are mounted in 10 groups so that
a condensation nucleus counter can measure the aerosol concentra-
tion upstream and downstream of each group.  Sinclair and Hoopes2
calibrated the screen diffusion battery.  The screen diffusion
battery must not be confused with the collimated holes structures
or tubular diffusion battery also described and calibrated by
Sinclair et al.3

     The continuous flow CNC was described and calibrated by
Agarwal and Sem.1*  The instrument first draws 300 cm3/min of
aerosol through a saturation chamber where the air becomes nearly
saturated with butanol at 35°C.  The nearly saturated aerosol
then passes through a 10°C condensation tube which condenses
butanol onto the particles, growing them into supermicron drop-
lets.  The droplets then pass through the sensing zone of a for-
ward scattering optical particle detector.  For concentrations
below 1000/cm3, the CNC measures particle concentration by count-
ing individual particles as they pass through the sensing zone.
The measurement in this range is a primary measurement, highly
accurate, with calibration required for only the constant sample
flow rate.  The lowest detectable concentration is limited only
by the time required to collect a statistically significant
sample.  Concentrations as low as 0.01/cm3 are automatically
displayed on the instrument's digital readout.  For concentra-
tions greater than 1000/cm3, the CNC measures the light scattered
in the forward direction by all particles simultaneously in the
sensing zone.  The photodetector output voltage is thus propor-
tional to particle number concentration.  Although accurate
calibration has been performed only as high as 6 x 105/cm3, this
calibration has been extrapolated above 106/cm3.

     The yalving system shown in Figure 1 between the diffusion
battery and the CNC has not been previously described.  The
purpose of the valving system is to allow a single CNC to sample,
in sequence, each of the sample ports of a diffusion battery.
The primary component of the valving system is a rotary valve
with 12 inlet ports and one outlet port.  The outlet port con-
nects directly to the inlet of the CNC.  The first inlet port
samples the aerosol entering the first stage of the diffusion
battery.  The next 10 sample downstream of each of the 10 dif-
fusion battery groups (or stages).  The twelfth port samples
air which has passed through a high-efficiency filter, serving
as a check on the zero level of the system.  Since the CNC re-
quires only 0.3 5,/min of sample aerosol flow, an auxiliary pump
and flow meter are built into the valving system to maintain
4 5,/min through the diffusion battery.

     The valving system can operate in any of three modes: manual,
one-cycle automatic, or continuous automatic.  In the manual
mode, the system remains on any diffusion battery port until
the operator or an externally-supplied signal commands it to
                               278

-------
proceed to the next port.  In the one-cycle automatic mode, the
system automatically steps through all 12 ports a single time,
then waits for a command to proceed through another single cycle.
In the continuous automatic mode, the system steps through all
12 ports as in the one-cycle mode, but then automatically con-
tinues cycling indefinitely.  The length of time on each port
can be adjusted from 5 to 50 s with 25 s being a typical time
required with the sizing system described here.  The valving
system may be set to skip all ports above any chosen port, a
time saving feature when measuring very small particles.  The
system generates a logic level signal, one second before stepping
to the next port, which can command an external recorder to ac-
cept data from the CNC.  An indicator and a recordable signal
indicate which port is being sampled at any given time.

     The design of the rotary valve is important for determining
the losses of particles passing through the system.  Passages
are about 4 mm diameter and 100 mm long through the rotary valve
itself with no other significant obstruction.  In addition, about
400 mm of 5 mm inside diameter vinyl tubing is necessary to con-
nect the diffusion battery to the CNC.  Table 1 shows the experi-
mentally measured losses in the entire valving system.  The mea-
sured size distribution can be corrected mathematically for these
losses.
           TABLE  1.   EXPERIMENTALLY  MEASURED LOSSES  OF
          PARTICLES  FLOWING  THROUGH  THE  SWITCHING VALVE
       	SYSTEM	

       Particle diameter,                Fractional loss,
             Dp,  urn                             %
0.008
0.010
0.015
0.02
0.03
0.05
0.07
0.10
30.9
25.4
14.2
10.5
7.6
3.5
2.9
2.0
                               279

-------
DIFFUSION BATTERY DATA REDUCTION

     The data reduction method used for the diffusion battery
was a slightly modified version of the non-linear iterative in-
version suggested by Twomey5 and adapted for use on diffusion
battery data by Knutson and Sinclair.1  The program, listed in
Appendix 1, was modified for this work by Kapadia.6  Since Knutson
and Sinclair1 describe the method in detail, this report will
only mention several characteristics.

     The particle size distributions in our work had a greater
range of variability than those measured by Knutson and Sinclair1
so Kapadia6 added a test for the quality of fit of the experi-
mental data with the computed solution.  After every five itera-
tions, the program calculates a chi squared value using the simu-
lated raw data which would exactly result in the computed solu-
tion and the actual experimental raw data.   When the chi squared
value is less than 0.001, the program prints the results and
stops.  It will also print results and stop if 105 cycles of
iteration have been completed before chi squared drops below
0.001.  In the latter case, the printed value of chi squared in-
dicates the quality of fit of the computed solution to the ex-
perimental data.

     The program uses the diffusion battery calibration of Sin-
clair et al.2'3 in a matrix developed by Kapadia.6  It also cor-
rects the CNC data for the detection efficiency using the CNC
efficiency data of Agarwal and Sem.1*  The program is set up for
use of an input data file so large batches of input data can
be processed rapidly.

     Table 2 is a typical printout of the program.  The first
upper column is diffusion battery port number and the second
upper column is corresponding CNC experimental concentration.
The third upper column is the ideal computed concentration which
would exactly result in the computed distribution.  The program
calculates chi squared, listed at the bottom of the printout,
from upper columns 2 and 3.  The first lower column lists the
geometric midpoint diameter, in micrometers, for each size in-
terval.  The second lower column lists corresponding number con-
centrations for each size interval in the form dN/d(log Dp) where
N is particle number concentration (per cm3) and Dp is particle
diameter  (micrometers).  The third and fourth lower columns are
surface and volume concentrations, respectively, calculated from
number concentration assuming perfectly spherical particles and
using a 45-interval size array rather than the normal 10-interval
array.  The bottom line of the lower columns, labeled  "totals",
is the total computed number, surface, and volume concentrations
in units of particles/cm3,  (micrometers)2/cm3, and  (micrometers)3/cm3,
respectively.  Notice that each of these values is the sum of
the appropriate column divided by four because each decade of
size contains four equal logarithmic intervals.
                               280

-------
ELECTRICAL AEROSOL ANALYZER AND ITS DATA REDUCTION

     The EAA has been used extensively during the past six years
for measurements of a variety of submicron aerosol size distri-
butions.  In the remainder of this report, the diffusion battery
particle sizing system is often compared with an electrical aero-
sol analyzer (EAA).  The EAA, its performance, and its data reduc-
tion have recently been described by Sem,7 Pui and Liu,8 and
Liu et al.9

     TABLE 2.   TYPICAL COMPUTER PRINTOUT FOR A SINGLE  PARTICLE
        SIZING  RUN OF THE DIFFUSION BATTERY AND CNC  SYSTEM
     TSI MODELS 3040  DIFF  BAT AND 3020 CNC  -  TWOMEY METHOD
     CNC ALCOHOL  9-10-79 RUN*2
     PORT
        0
        1
        2
        3
        4
        5
        6
        7
        8
        9
        10
NO,
CNC DATA
270000,
250000.
207000.
154000.
106000.
 78500.
 55700.
 37000.
 23800.
 15700.
 10100.
CALC DATA
270953.
245133.
202539.
155325.
112654.
 78617.
 53501.
 35829.
 23748.
 15635.
 10252.
      hID  PT.  DIA

        .0042
        .0075
        .0133
        .0237
        ,0422
        .0750
        .1334
        .2371
        .4217
        .7499
      TOTALS
           DNDLGD
                DSDLGD
                                                DVDLGD
7. 132E-03
9.697E+01
4.078E+04
3.204E+05
4 , 134E+05
2.710E+05
5.885E+04
4.724E+03
3.438E+02
4.443E+01
2.774E+05
3.982E-07
1.712E-02
2.277E+01
5.657E+02
2.308E+03
4.785E+03
3.286E+03
8.341E+02
1.920E+02
7.845E+01
3.019E+03
2.797E-10
2. 139E-05
5.057E-02
2.235E+00
1 .621E+01
5.976E+01
7.299E+01
3.295E+01
1.348E+01
9.799E+00
5.208E+01
      NO.  OF ITERATIONS= 105
                       CHISQ=  1.610E-02
                               281

-------
     Several computerized procedures have been developed for
reducing EAA data.  The one used in this study uses the same
Twomey5 method described earlier for the diffusion battery.
Appendix 2 is a listing of the program as adapted to the EAA
by Kapadia.6  Table 3 shows a typical printout of the results
from the program.  The printout format is the same as described
earlier for the diffusion battery printout.   This program is
much faster than several previous EAA programs and appears to
result in lower chi squared values  (better fits)  than most other
methods.

    TABLE 3.  TYPICAL COMPUTER PRINTOUT FOR A SINGLE PARTICLE
         SIZING RUN OF THE ELECTRICAL AEROSOL ANALYZER
      TSI MODEL 3030   EAA   -  TWOMEY METHOD

      EAA ALCOHOL 9-10-79  RUN*2A

       DIA,        EAA DATA        CALC DATA
       .0032
       .0056
       .0100
       .0178
       .0316
       .0562
       .1000
       .1778
       .3162
       .5623
      1.0000
3,310
3.310
3.310
3.290
2.790
2,310
1.090
 .320
 .100
 .020
0.000
 3.308
 3.308
 3,308
 3.288
 2.788
 2.306
 1.095
  .317
  .090
  .027
  .009
      MID  PT.  DIA

         .0042
         .0075
         .0133
         .0237
         .0422
         .0750
         .1334
         .2371
         .4217
         .7499
      TOTALS
DNDLGD
DSDLGD
DVDLGD
0.
0.
1 .879E4-04
2. 166E+05
2.983E+05
2.980E+05
9.479E+04
1.357E+04
1 .257E+03
3.636E+00
2.353E+05
0.
0.
1 .OSOEtOl
3.826E+02
1 .666E+03
5.264E+03
5.296E+03
2.397E+03
7.025E+02
6.423E+00
3.931E+03
0.
0.
2.333E-02
1.512E+00
1 . 171E+01
6.579E+01
1.177E+02
9.473E+01
4.937Ei01
8.028E-01
8.541E+01
      NO.  OF  ITERATIONS=  20
             CHISQ=  4.201E-03
                               282

-------
DESCRIPTION OF THE  EXPERIMENT

     As with any  aerosol  measurement,  the delivery of the sample
to the diffusion  battery  and  EAA must  be done carefully.  Par-
ticles larger than  0.2  ym can be lost  in the sample tube by  in-
ertial impaction  and  gravitational settling while particles
smaller than 0.03 ym  can  be lost or changed by diffusion to  the
walls or to each  other.   All  particles can be changed drastically
by evaporation or condensation of volatile components.

     Figure 2 illustrates the major components of the aerosol
generation and sampling system for a set of experiments involv-
ing atomized aerosols.  Compressed air was regulated, dried,
and filtered before entering  the aerosol generator, a stable,
single-jet atomizer.  The output of the atomizer was a stream
of droplets which could be mixed with  clean dilution air before
the droplet aerosol entered a diffusion dryer.  The dryer con-
sisted of a straight, 12-mm diameter tube made from stainless
steel screen and  surrounded by silica  gel.  Water or alcohol
vapor diffused rapidly  to the silica gel while the dried aerosol
particles passed  through.  The dry aerosol then entered a Kr-
85 electrostatic  neutralizer  which exposed the particles to  high
SWITCHING
VALVE
MODEL 3042
h

CNC
MODEL 3020
  4L/mim
EXCESS .
AEROSOL'
4L/mirf
EAA




FROM ROOM
1 	 ^
ELECTROSTATIC
NEUTRALIZER
MODEL 3012

EAA
MODEL 303O
D

LUTION'VO' VALVE
DIFFUSION
DRYER
MODEL 3062
-*
^
3.5

ATOMIZER
MODEL 3076




AIR SUPPLY
(CLEAN, DRY
REGULATED AIR)
MODEL 3074

                                                             _COMPRESSED
                                                                AIR
           Figure 2. Schematic diagram of the aerosol generation and measurement
                  system for the atomized aerosols.
                                283

-------
concentrations of positive and negative ions, allowing  the  par-
ticles to attract neutralizing ions.  The dry, neutralized  aero-
sol then entered a mixing  and damping manifold where  it was avail-
able to the diffusion  battery and EAA inlets.  Excess aerosol
was dumped from the  manifold to the atmosphere.

     The diffusion battery and EAA sampled simultaneously from
the manifold, each at  its  normal 4 5,/min aerosol sample rate.
The sample lines were  less than 40 cm long, as short  as possible.
It was especially important to mix the aerosol well before  it
entered the diffusion  battery so that its first sampling port
sampled mixed aerosol  rather than aerosol from the boundary layer
with lower particle  concentration.  An elbow in the sample  line
within 10 cm of the  diffusion battery inlet seems to  provide
sufficient mixing.   The EAA drew its sheath air from  the room.
Data was recorded continuously on a two-pen strip chart recorder.
The diffusion battery  system required about 4 minutes per com-
plete sizing run while the EAA required about 2 minutes.

     Figure 3 illustrates  the major components of the aerosol
generation and sampling system for a set of experiments involving
combustion aerosols.   The  major difference from the system  shown
in Figure 2 is the replacement of the entire generator  by a 1-m3
plastic bag.  The bag  was  nearly filled first with either room
               4L/miru ,
                4L/mirf
                                 PLASTIC BAG
             EAA
           SHEATH AIR
           FROM ROOM
         Figure 3. Schematic diagram of the aerosol generation and measurement
               system for the welding smoke and propane aerosols.
                                284

-------
air or dried, filtered air.  Then the combustion aerosol was
introduced, in the case of welding smoke aerosol by drawing it
into a large volume centrifugal blower and exhausting  it into
the nearly full bag, and in the case of propane aerosol by in-
serting the burning propane torch directly into the bag for about
10 s.  The intent was not to characterize the combustion aerosol
generation process, but rather to produce a representative aero-
sol in the bag which could challenge the diffusion battery and
EAA simultaneously.  By qualitatively varying the smoke intro-
duction method, we could supply the bag with a variety of aerosol
concentrations and with number median diameters in the 0.005
to 0.2 ym range.

     The experimental results below are bar graphs of  the mea-
sured concentration within each size range of the two measurement
systems.  The error bars represent the maximum range of variation
observed in the experimental measurements.  In some aerosol decay
experiments, only one measurement was possible at a given point
in time so no error bars are shown.  Usually, we made  two EAA
size distribution measurements during a single diffusion battery
measurement.

     In addition to the programs listed in Appendices  1 and 2,
we corrected both the diffusion battery and the EAA data to ac-
count for the exponential decay of the combustion aerosols while
the sizing runs of several minutes duration were underway.

EXPERIMENTAL RESULTS AND DISCUSSION

     The first aerosol we will discuss is the dry residue par-
ticles from the atomization of clean, unused, reagent  grade
isopropanol.  Figure 4 shows the measured number of distributions,
The diffusion battery measured three distributions in  12 minutes
while the EAA measured six distributions during that time.  Both
systems measured repeatably.  The diffusion battery and EAA
measured similar distributions with a tendency for the EAA to
measure slightly larger sizes.  Figure 5 shows the same data
converted to volume distributions by assuming spherical particles,
If the spheres have unit density, the vertical axis is equal
to mass concentration in micrograms per m3.  Figure 6  shows the
same data on a log-normal plot.  The measurements of both instru-
ments were nearly log-normal with both measuring a geometric
standard deviation of 1.85.  The diffusion battery system mea-
sured a number median diameter of 0.041 ym and the EAA measured
0.048 ym.  This aerosol spans the central portion of the size
range where each measurement method is most accurate.  The re-
sults indicate good agreement.

     Fig.ire 7 shows the results of the next set of comparative
measurements.  The atomizer system generated aerosol from a 0.1%
(by volume)  solution of DOP in isopropanol.   Again, the results
from the two measurement methods are similar.  The results are
                               285

-------
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                                            --A-
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Figure 4.  Number distributions measured by diffusion battery and EAA of

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            of aerosols atomized from 100% isopropanol.
                                 286

-------
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Figure 7.  Number distributions measured by diffusion battery and EAA
          of aerosols atomized from 0.1% OOP in isopropanol.
                                287

-------
nearly log-normal  with  geometric standard deviations  of  1.5 and
number median diameters of 0.10 ym for the diffusion  battery
system and 0.13  ym for  the EAA .

     Next, we measured  aerosol generated by the  atomizer system
from a solution  of 1.0  g NaCl in 1000 cm3 of distilled water.
Figure 8 shows the results.   Both instruments measured the mode
in the distribution at  the same particle diameter.  However,
while the EAA results are very nearly log-normal with number
median diameter  of 0.06 ym and geometric standard  deviation of
1.8, the diffusion battery results are not log-normal.   The dif-
fusion battery appears  to "chop off"  some of  the particles  above
0.2 ym.

     We also measured aerosol generated by the atomizer  from
10 g NaCl in 1000  cm3 of distilled water.  Figure  9 shows the
results.  Again, both instruments locate the mode  correctly.
The EAA results  are nearly log-normal with number  median diameter
of 0.08 ym and geometric standard deviation of 1.8.   The dif-
fusion battery results  are not log-normal probably because of
the collection of  particles above 0.2 ym by impaction and gravi-
tational settling  in addition to diffusion.  The data reduction
program does not consider these additional collection mechanisms.
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                of aerosols atomized from 0.1% NaCl in distilled water.
                                288

-------
     For the next  experiment, we used the bag  sampling system
to sample diluted  smoke from an electric arc welding  process.
Figures 10 and  11  show the results of the diffusion battery and
EAA measurements,  respectively.  The two runs,  in  each case, were
12 minutes apart.   The EAA results for Run  1 show  a definite
bimodal shape  in the  number distribution with  a small combustion
mode near 0.03  jam  and a larger mode in the  accumulation range
around 0.2 ym.  Twelve minutes later, the smaller  mode has dis-
appeared and the accumulation mode has also decayed.   However,
the range around 0.075 ym shows no change,  probably the result
of the smaller  particles colliding and growing  into the inter-
mediate range.  While the diffusion battery results show a hint
of similar tendencies, the data is not nearly  so clear, probably
because of the  limited resolution of the measurement.

     The final  experiment reported here was the measurement of
very small particles  near the lower size limit  of  both measure-
ment systems.   We  first filled the bag with clean  dry air (CNC
measured 200 particles/cm3, EAA measured nothing).   Then we pro-
duced a very fresh aerosol by inserting a propane  torch into
the bag for about  10  s.  We then closed the bag and immediately
began measurements.   Figure 12 shows the volume distributions
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         Figure 9. Number distributions measured by diffusion battery and EAA
                of aerosols atomized from 1% NaCI in distilled water.
                                289

-------
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Figure 10.  Number distributions measured by diffusion battery of diluted

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 Figure 11.  Number distributions measured by EAA  of diluted welding

             smoke in a closed container as the aerosol ages.
                                  290

-------
measured by  the  EAA beginning just  after  the bag was filled,
four minutes  later, and four more minutes later.  Additional
measurements  were made by the EAA at  two-minute intervals,  but
are not plotted  on Figure 12 for clarity.  We can clearly  see
some interesting coagulation growth as  the aerosol ages.   In
Figure 13, we see the volume concentration observed in three
size channels of the EAA:  the channels from 0.0056 to 0.01 um,
from 0.01  to  0.178 ym, and from 0.1 to  0.178 ym.  The smallest
channel coagulates quickly and the  next smallest less quickly.
The concentration in the largest channel  increases as aerosol
accumulates  in that size range, having  grown from smaller  sizes.
Incidentally, we extrapolated the EAA sensitivity curve  of Pui
and Liu8 to  obtain a number concentration in the 0.0032  to
0.0056 ym  range.  Although this may result in poor absolute ac-
curacy, comparison from run to run  is valid.

     Figure  14 shows diffusion battery  results from the  propane
aerosol.   The decay of the aerosol  is evident, but not as  clear
as with the  EAA.  The four-minute requirement for a single sizing
run limits the diffusion battery in this  experiment.  Also, the
CNC does not  effectively detect particles below 0.01 ym, limiting
the diffusion battery-CNC system at present to the range above
0.01 ym.
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                                  • RUN 5, t-8-10minutes
                         -1
   .004  .007 .01    .02    .04   .07  O.I    0.2    0.4
             PARTICLE DIAMETER, Dp, MICROMETERS
                                                     0.7 1.0
          Figure 12.  Volume distributions measured by EAA of fresh propane
                   aerosol in a closed container as the aerosol ages.
                                291

-------
            IO.O
   7.O
10
 E

•^4.0
 a.
 a.
 o

 £20

-------
CONCLUSIONS

     A new aerosol size measuring system has been developed con-
sisting of a compact multiple screen diffusion battery, a con-
tinuous flow condensation nucleus counter, and an automatic
rotary valve to switch the inlet of the CNC to each of the dif-
fusion battery exit ports.

     A simple computer program has been developed to convert
the data from the new sizing system into submicron particle size
distribution.  The same approach has been used to calculate par-
ticle size distributions for the electrical aerosol analyzer.

     In an experimental comparison of the new diffusion battery
system with an electrical aerosol analyzer, we find good com-
parison in the range from 0.01 to 0.2 urn for most aerosols tested,
Both systems locate the peak in the size distributions within
that range.  The diffusion battery system combined with the new
computer program appears to cut off part of measured size distri-
butions above 0.2 urn as evidenced by its inability to correctly
measure log-normal distributions in the range around 0.2 ym.
Further work is needed on data reduction methods for the dif-
fusion battery to include the effects of inertial impaction and
gravitational settling for particles greater than 0.2 ym.  The
diffusion battery-CNC system also needs further evaluation to
determine particle losses below 0.01 ym.  The current system
cannot effectively measure particles below 0.01 ym because of
this difficulty.  On the other hand, the EAA can measure par-
ticles below 0.01 ym in circumstances where few large particles
exist.  The above example of the measurement of fresh propane
torch aerosol demonstrates the EAA's usefulness for measuring
coagulation rates for such aerosols below 0.01 ym.

ACKNOWLEDGEMENTS

     We received considerable assistance with the experiment
and with data reduction from Richard Remiarz.  Abde Kapadia
shared his computer programs with us soon after he developed
them.  We are grateful for this generous assistance.
                               293

-------
REFERENCES

1.   Knutson, E.O.,  and D. Sinclair.   Experience in Sampling
     Urban Aerosols  with the Sinclair Diffusion Battery and
     Nucleus Counter.  In: Proceedings:  Advances in Particle
     Sampling and Measurement.  W.B.  Smith, compiler.  EPA-600/7-
     79-065, U.S. Environmental Protection Agency, Research
     Triangle Park,  NC, 1979.  pp. 98-120.

2.   Sinclair, D., and G.S. Hoopes.  A Novel Form of Diffusion
     Battery.  Am. Ind. Hyg. Assoc. J. 36:39-42, 1975.

3.   Sinclair, D., R.J. Countess, B.Y.H. Liu, and D.Y.H. Pui.
     Automatic Analysis of Submicron Aerosols.  In:  Aerosol
     Measurements, D.A. Lundgren et al., eds.  University Presses
     of Florida, Gainesville, 1979.

4.   Agarwal, J.K.,  and G.J. Sem.  Continuous Flow, Single-Particle-
     Counting Condensation Nucleus Counter.  Submitted to J.
     Aerosol Sci., 1979.

5.   Twomey, S.  Comparison of Constrained Linear Inversion and
     an Iterative Nonlinear Algorithm Applied to the Indirect
     Estimation of Particle Size Distributions.  J. Comput. Phys.
     13:188-200, 1975.

6.   Kapadia, A.  Ph.D. Thesis, University of Minnesota, Mechani-
     cal Engineering Department, Minneapolis, 1979.

7.   Sem, G.J.  Electrical Aerosol Analyzer:  Operation, Mainten-
     ance, and Application.  In:  Aerosol Measurements, D.A.
     Lundgren et al., eds.  University Presses of Florida, Gaines-
     ville, 1979.

8.   Pui, D.Y.H., and B.Y.H. Liu.  Electrical Aerosol Analyzer:
     Calibration and Performance.  In:  Aerosol Measurements,
     D.A. Lundgren et al., eds.  University Presses of Florida,
     Gainesville, 1979.

9.   Liu, B.Y.H., D.Y.H Pui, and A. Kapadia.  Electrical Aerosol
     Analyzer:  History, Principle, and Data Reduction.  In:
     Aerosol Measurements, D.A. Lundgren et al., eds.  University
     Presses of Florida, Gainesville,  1979.
                               294

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                                     APPENDIX  1
       PROGRAM DIFFBATdNPUT,OUTPUT)
C      DIFFBAT USES TUOMEY'S NON-LINEAR ALGORITHM FOR REDUCING DIFFUSION
C      BATTERY DATA. THIS PROGRAM CAN BE USED FOR THE TSI SCREEN BATTERY
C      FOR 4.0 LPM FLOW RATE, THE ITERATIVE PROCEDURE IS STOPPED EITHER
C      WHEN CHI-SQUARE IS LESS THAN 0.001 OR THE NUMBER OF ITRATIONS IS
C      GREATER THAN 100, WHICHEVER OCCURS FIRST AFTER THE FIRST 20
C      ITERATIONS.
C
C      THIS PROGRAM WAS WRITTEN BY ABDE KAPADIA , A PH.D CANDIDATE AT THE
C      U OF M.
        COMMON CALIB<12,45),KDAT,DAT(12)»CDAT(12),CLOSS<45>,
     •f ITER,FLOW,DIA<45> r X > ACTDAT < 11 )
       DIMENSION CALDATU1)
       DIA(1)=0.00316228
       DPMULT=1.154781985
       DO 5 J=2.45
 5     DIA DAT(J)=0.0
       DAT(11)=ACTDAT(11>
       CALL DIFFTWO
       CALDAT<11)=CDAT<11>
       DO 73 1=1,10
 73    CALriAT(ll-I)=CALDAT(12-I)+CDAT(ll-I)
      PRINT 78
78    FORMATdX,1  1,//1X,"TSI MODELS 3040 DIFF BAT AND 3020 CMC  -  TWO
     +MEY METHOD1)
       PRINT 81,TITLE1,TITLE2,TITLE3,TITLE4
 81    FORMAT(/1X,4A10,//1X,'PORT NO.',5X,'CNC DATA1,
     + 8X,'CALC DATA1)
       DO 85 1=1,11
       J=I-1
       PRINT 83,J,ACTDAT(I),CALDAT(I )
 83    FORMAT(3X,I2,8XFF8.0,8X,F8.0)
85     CONTINUE
C
C      CALCULATE VALUES FOR OUTPUT
C
       DO 100 J=3,39,4
 100   CLOSS(J)=(0.5*CLOSS(J-2)+CLOSS(J-i)+CLOSS(J)      +
     + CLOSS(J+l)+0.5*CLOSS(J+2))*4.0
       DO 110 J=3,43,4
        CLOSS(J+1)=CLOSS(J)*3.14*(DIA(J>**2>
 110   CLOSS(J-t-2)=CLOSS< J ) *0 . 523* ( DIA ( J)**3)
       TNUM=0.0
       TSURF=0.0
       TVOL=0.0
                                         295

-------
                                APPENDIX 1  (cont)
       DO 120 J=3?43?4
       TNUM=TNUM+CLOSS(J)
       TSURF = TSURF + CLOSS(J+l )
 120   TVOL=TVOL+CLOSS(J+2)
       PRINT 130
 130   FORMAT(//1X?'MID PT. DIA1,4X?'DNDLGH'?7X?'DSDLGD'?7X?'DVDLGD1,/)
       DO 150 J=3?39?4
 150   PRINT 160?DIA?CLOSS(J)?CLOSS(J+l)?CLOSS(J+2)
 160   FORMAT<2X,F6.4?2X?3(4XrlPE9.3)>
       TNUM=TNUh/4.0
       TSURF=TSURF/4.0
       TVOL = TVOL./4.0
       PRINT 190?TNUM?TSURF?TVOL
 190   FORMAT1PE9.3>)
       PRINT 192»ITER»X
 192   FORMAT(//1X»'NO. OF  ITERATIONS= '»13»5X»'CHISQ=  '.1PE10.3)
       DO 195 J=3»39f4
 195   CLOSS(J)=CLOSS.120?.151?,29?.3D?.47?.59?.6??
     + .77?.83?.90?.95?,97»29*1.O/
       KMAX=20
       JMAX=45
       DO 10 J=1?JMAX
 10    CLOSS(J)=AC1DAT(1)/JMAX
       ITER=0
 100   DO 20 K=1?KMAX
       DO 30 I=1?NDAT
       RATIO=0.0
       DO 40 J=1»JMAX
 40    RATIO=RATIO+CALIB(I»J)*CLOSS(J)*CNCEFF(J)
       IF(RATIO) 30?30?60
 60    RATIO = DAT(I)/RATIO-l ,0
       DO 70 J=1?JMAX
 70    CLOSS(J)=CLOSS(J)*(l.0+(RATIO*CALIB(I.J) ) )
 30    CONTINUE
 20    CONTINUE
       ITER=ITER+KMAX
       IF
-------
                                APPENDIX 1  (cont)
c
C      THIS SUBROUTINE COMPUTES THE LOSS MATRIX FOR TSI SCREEN BATTERY
C      FOR 4.0 FLOW RATES
C
C
       SUBROUTINE TSI
        COMMON CALIB(12>45)rKDAT.DAT(12)rCDAT(12)»
     •f CLOSS(45)fITER»FLOUfDIA(45)rXrACTDATdl)
       FLOW=4.0
 60    AK1=-1.14423
        CKl=-2.990605
 70    DO 90 J=l»45
       NSCRN=0
       SLOPE=-10.0**(AK1*ALOG10(DIA(J»+CM)
       DO 80 1=2.11
        CALIBlI-l»J)=(10.0**(SLOPE*NSCRN))-(10.0**(SLOPE*(NSCRN+I-1>))
 80    NSCRN=NSCRN+I-1
 90    CALIBdl t J) = 10.0**(SLOPE*55. >
       RETURN
       END
C
C      ACHISQ
C
C      THIS SUBROUTINE COMPUTES THE  CHI-SQUARE FOR  THE  OBSERVED
C      AND CALCULATED DATA FOR THE DIFFUSION  BATTERY.
C
Lf
       SUBROUTINE ACHISQ
        COMMON CALIBd2f45)fKDAT»DAT(12)»CDAT(12)»
     + CLOSSC45) , ITER.FLOU»DIA(45> rX.ACTDATdl )
       X=0.0
       TCDAT=0.0
       DO 5 J=liKDAT
 5     TCDAT=TCDAT+CDAT
       DO 10 J=liKDAT
       AF=(CDAT(J)/TCDAT)-(nAT(J)/ACTnAT(l))
       IF(ABS(AF)  ,LT. .001 .AND.  CDAT(J)  .LT.  .0001) GO TO  10
       X = X-KAF**2)/(CDAT( J)/TCDAT)
 10    CONTINUE
       RETURN
       END
*RDY*
                                        297

-------
                                    APPENDIX 2
    .  PROGRAM  EAATWOCINPUT.OUTPUT)
      COMMON /EAADAT/PHK 11,45) rCURKll) ,CUR2<11> ,X,
     + ITER,DIA<45),EDN<10>,EDS(10),EDV(10)
      DIMENSION  COMCUR(ll) , SENS< 45) >PC1 < 45) ,PC2<45> ,DNI(1L) ,
     + EAACURdl ) , DNDIUO)
      DATA DIA/.00316228,.00365174,.00421697,.00486968,.00562342,
     •f .00649382,.00749895,.00865965,.01000001,.01154783,.01333522,
     + .01539928,.01778281,.02053527,.02371375,.02738422,.03162230,
     + .03651744,.04216968,.04869679,.05623417,.06493821,.07498948,
     + .08659650, .10000007,.11547828,.13335224,.15399227,.17782807,
     + .20535266,.23713755,.27384217,.31622800,.36517440,.42169682,
     t .48696789,.56234175,.64938212,.74989477,.86596497,1.00000075,
     + 1.15478285,1.33352243,1.53992768,1.77828075/
      DATA DNHI/0.0,9.52E6,4.17E5,1.67E5,8.70E4,4.44E4,2.41E4,
     + 1.23E4,6.67E3,3.51E3/
      DATA JMAX,I MAX,PI/45,11,3.14167
      DO 140 J=1,JMAX
      TMP=IHA(J)-.0125
      IF  120,130,130
120   SENS( J)=2.351E6*(DIA(J))**6.262
      GO TO 140
130   SENS  GO TO 230
      DO 20 J=1,JMAX
      PC2( J)=EAACURU)/JMAX
20    CONTINUE
      TCUR=EAACUR<1)
      IMAX1=IMAX-1
      DO 30 I=1,IMAX1
      CUR1(I)=EAACUR(I)-EAACUR<1 + 1 )
      CUR1(I)=AMAXKCURKI) ,0.0)
30    CONTINUE
      CUR1(IMAX)=EAACUR(IMAX)
      ITER=0
      KMAX=20
      TCUR=0.0
      DO 32 I=1,IMAX
      TCUR=TCUR-fCURKI)
32    CONTINUE
35    DO 60 K=1,KMAX
      DO 40 J=1,JMAX
      PCK J)=PC2(.J)
40    CONTINUE
      DO 55 I=t,IMAX
      A = 0.0
      DO 50 J=1,JMAX
      A = A + PHH I, J)*PC2( J)
50    CONTINUE
      IF(A) 55,55,54
54    A=CUR1(I)/A-1.0
      DO 61 J=1,JMAX
      PC2( J)=PC2< J)*<1.0 + A*PHKI, J) )
61    CONTINUE
55    CONTINUE
60    CONTINUE
      DO 70 I=1,IMAX
                                         298

-------
                                APPENDIX 2  (cont)
      CUR2=0.0
      DO 65 J=1»JMAX
      CUR2
65    CONTINUE
70    CONTINUE
      IF+PCK3) + .
      IF = /2.0 + PCK J-1)+PCK
     + PCKJ + D+PCK J+2>/2.0>
      IF (PCK J) .LT.1E-05) PCK J) =0.0
111   CONTINUE
      PCK42) = ( .5*PCK40)+PCK41 )+PCl (42) +
     + PCK43)+PCK44)+PCK45) >
      IF GO TO 220
      IF(CURKI) .LT. ,001*TCUR> GO TO 220
      J=I*4-2
      DNI(I)=PC1=0.0
210   CONTINUE
C
r
      PRINT 704
704   FORMATdX,'  -,//lXf'TSI MODEL 3030  EAA  -  TUOMEY METHOD')
      PRINT 705»TITLElfTITLE2rTITLESfTITLE4
/05   FORMAT(/lXf4A10f//2XTlniA.1>8Xf-EAA DATA'.
     + SXr'CALC  DATA'/)
      COhCUR(ll)=CUR2(ll)
      DO 221  I=1*IMAX
      CO«CUR(11-I)=COMCUR(12-I)+CUR2(11-I)
221   CONTINUE
      DO 222  I=lrIMAX
      PRINT 706.DIA<4*1-3).EAACUR(I).COMCUP(I)
706   FOftMAT(IX»F6.4.2<8X.F6.3>)
222   CONTINUE
      DO 225  I=1.IMAX1
      EDN(I)=CUR1
-------
                                APPENDIX 2  (cont)
      PRINT 706.DIA(4*I-3> .EAACUR(I)
227   CONTINUE
      CALL WRTOUT(O)
      GO TO 145
300   STOP
      END
C
C
      SUBROUTINE ACHISQ
      COMMON /EAADAT/PHKll .45) .CUR1 < 1 1 > «CUR2< 1 1 > »X.
     + ITER»DIA(45)»EDN<10) .EDS( 10) »EDV< 10 >
      TCUR1=0,0
      TCUR2=0.0
      IMAX=11
      X=0.0
      DO 10 I=1.IMAX
      TCUR1=TCUR1+CUR1(I)
      TCUR2=TCUR2+CUR2(I)
10    CONTINUE
      DO 20 I=1.IMAX
      ACUR2=CUR2(I)/TCUR2
      AF=(CUR1( D/TCURD-ACUR2
      ABSAF=ABS .EDNUO) .EDS (10) >EDV<10)
      PRINT 710
710   FORMAT 7X , • DSDLGD • r 7X , • DVDLGD* > /)
      TEDN=0.0
      TEPS=O.O
      TEDV=0.()
      DO 100 I=l»10
      PRINT 711rDIA< 4*1-1) »EDN
-------
                             PAPER 17


             AN  IN-SITU  LIQUID DROPLET  SIZING  SYSTEM
                         DANIEL E. MAGNUS
                          DAVID  S.  MAHLER
                       KLD ASSOCIATES, INC.
ABSTRACT
     The development of an in-situ device for measuring the size
and concentration of liquid droplets is described.  The sensing
element or probe is a hot wire approximately 5 ym in diameter
and 1 mm long.  When droplets impact the hot wire, the resultant
electronic signal is a diagnostic for the droplet size.  An elec-
tronic processing system was implemented to analyze automatically
the signals and determine the droplet size distribution (number
of droplets in each of 14 independent size intervals).  For each
sample run, the entire distribution is determined, and subsequent
off-line processing is used to compute the droplet concentration
and/or entrained mass.

     The measuring system is called the DC-2 and was developed
under the sponsorship of the EPA.  The device has been used to
evaluate efficiency of demisters used to remove entrained mass
from various types of scrubbers.  The device has also been suc-
cessfully demonstrated in cooling tower studies and the measure-
ment of oil droplet distributions and selected acid mists.

     The technology to improve the performance of the probe and
to interface the system with a microprocessor is discussed.

INTRODUCTION

     In 1974 KLD Associates, Inc. developed and successfully
demonstrated an instrument using the hot-wire principle for
measuring the size and concentration of liquid droplets in a
gas stream.  The demonstration of the device included both labora-
tory and field measurements.  Originally the device was designed
for the droplet size range from 20 urn to 500 ym.  However, the
field studies showed the importance of measurements  in the
range from 1 ym to 100 ym, where a majority of the droplets are
found.  Based upon these studies, the electronics of the  system
was redesigned to include droplets in the size range from 1 ym
to 600 ym.
                               302

-------
     Under a contract from the Environmental Protection Agency,
the apparatus for the measurement of droplets was to be improved
and refined to enable in-situ measurements under adverse field
conditions.  The desired improvements in this area of technology
included:

        reducing the number of adjustments to be performed by
        the operator and providing for automatic data acquisi-
        tion,

        providing 14 sub-intervals of droplet sizes over the
        range from 1 ym to 600 ym,

        building into the electronics the calibration curve for
        droplet size and displaying the results in digital form
        in engineering units, and

        improving the ruggedness of the probe to make it more
        suitable for field measurements.

     The above design objectives were incorporated into a droplet
measuring device which is designated as the DC-2.  The purpose
of this paper is to describe the results of this design effort
and to discuss both laboratory and field results achieved with
the equipment.  Also presented are some recent new design
activities to interface the device with on-line computers.

PRINCIPLE OF OPERATION

     The operation of the heat transfer droplet sensor is based
on the local cooling caused by a droplet attaching to a hot wire.
The concept  is schematically shown in Figure 1, where the hot
wire and its longitudinal temperature distribution are shown
(a) before a water droplet  (cross-hatched circle) interacts with
the wire.  The electrical resistance of the wire in  (a) is high
and substantially uniform along the wire.  In situation  (b),
the portion  of the wire covered by the droplet is cooled to ap-
proximately  the droplet temperature.  With a constant electrical
current heating the wire, a measurable voltage drop can be sensed
between the  wire supports.  The voltage for condition  (a)  (be-
fore the droplet attachment) is reduced in direct proportion
to the cooled length of wire, i.e., the droplet diameter  (con-
dition b).   The electrical energy delivered to the wire evapo-
rates the water, leaving the sensor dry and ready for further
interactions with droplets.

     The above description of the operating principle for the
hot wire probe is an idealization and in actual practice the
electrical signal is rather complex.  A typical electrical signal
obtained during a droplet-hot wire interaction is shown in Fig-
ure 2.  Reduction of the voltage implies cooling of the wire.
An initial fast decay of the signal is observed; it corresponds
                              303

-------
                     • SUPPORT
                                                     SUPPORT
                                     •HOTWIRE
WIRE TEMPERATURE

       i

    HOT- •
AMBIENT
                                                     WIRE LONGITUDINAL
                                                     DIMENSION
                        (a) TEMPERATURE BEFORE ATTACHMENT
 WIRE TEMPERATURE
    HOT-
AMBIENT
                                                      WIRE LONGITUDINAL
                                                      DIMENSION
                         (b) TEMPERATURE AFTER ATTACHMENT

                   Figure 1.  Principle of operation of the sensor.
                                     304

-------
                  VOLTAGE
U>
O
DROPLET
WIRE
CONTACT
                          LONGITUDINAL
                          COOLING
                                                                          DROPLET EVAPORATION
                                                                                                                      TIME
                                            Figure 2.  Electrical signal from sensor.

-------
to the initial contact of the droplet and  the wire.   During  this
period the wire is cooled radially and rapidly  assumes  the  tem-
perature of the droplet.  The duration of  this  portion  is of
the order of a few microseconds.  Following  the initial contact,
the signal changes more slowly as the droplet centers itself
around the wire and as longitudinal cooling  of  the  wire takes
place.  During this period of the interaction,  a warming of  the
droplet/wire takes place, raising the signal until  the  boiling
temperature is reached; the droplet shrinks  due to  evaporation
and then disappears.  The voltage in the wire then  returns  to
the equilibrium level prior to the interaction  of the droplet.

     The foregoing concept of measuring droplet size  and concen-
tration is implemented using two major components:  a hot wire
probe as a transducer and electronic instrumentation  for analyz-
ing the electrical signals for droplet size  and storing the  data,
These components are shown in Figure 3.
                     Figure 3. Droplet counter and probe.
                               306

-------
     The probe is made from platinum wire 5 urn in diameter, and
the active portion of the wire is one millimeter long.  With
this size wire, the DC-2 can measure diameters of droplets from
1 ym to 600 ym.  As shown in Figure 3, the fine wire is mounted
across a ring at the top of the transducer, which is connected
to the instrumentation box by a single coaxial cable.  This type
of probe is called an open probe since it is unprotected against
breakage during handling.  Other designs have been fabricated
with sliding sleeves which cover the probe and successfully
minimize damage from handling.

     The electronics box for analyzing the signals from the probe
determines the size of the interacting droplet with respect to
14 size ranges and permanently stores the count for each range.
The size ranges can be adjusted by changing a plug-in ladder
network.  The DC-2 comes equipped with four ladder networks,
and thereby allows the operators to study a variety of droplet
distributions.  The equipment is designed for simple operation
and a single pushbutton switch (START) automatically cycles the
DC-2.  When the START switch is pushed, the device remains in
the droplet counting mode until a preselected number of drop-
lets (100, 1,000 or 10,000) interact with the probe or a pre-
scribed time limit (10, 100, 1,000 seconds) is reached.  After
completing a measurement cycle, the system halts and the data
can be read from a liquid crystal display, which was chosen for
its superior performance in bright ambient light.

     The electronics box has been designed to provide the field
user with a light-weight and compact instrument.  The box is
14% in. long, 6 in. wide, and approximately 6 in. high and
weighs approximately 10 Ibs.  The case and card bucket are made
of drawn aluminum; the circuit cards are wire-wrapped and made
of glass epoxy.  The instrument is powered from 125VAC (± 15%),
60 Hz line requiring 2.5 watts of power.  The electronic system
is designed using low power, CMOS logic with a maximum counting
rate of 500 droplets/sec.  In the report by Medecki, et al.,
a description of the logic and circuit diagrams is presented.1

LABORATORY INVESTIGATIONS

     Laboratory investigations with the DC-2 have emphasized
three types of activity:

        droplet attachment mechanism

     •  calibration procedures

        comparisons with other droplet measurement techniques

     For the first two types of activity, attachment mechanisms
and calibration, carefully controlled procedures for generating
                               307

-------
droplets are required as well as reliable techniques for record-
ing and verifying the droplets interacting with the hot wire
probe.  A variety of techniques were used to generate monodis-
persions and polydispersions of droplets.  These techniques in-
cluded:  saturated steam, vibrating capillary, micropump, rotat-
ing disc, Berglund Liu generator, and various nozzles.  The mono-
dispersion generated with the Berglund Liu apparatus was most
useful for developing the initial calibration curve for the de-
vice.  However, the available size range was restricted and there-
fore other techniques were used to extend the range of calibra-
tion.  Working with a polydispersion, the interacting droplets
are observed under a microscope during attachment to the hot
wire.

     A photographic camera records the image of both the wire
and the droplet, and a permanent record is obtained to study
the attachment mechanism and to provide the calibration data.
Since the interaction time is short, an electronic flash is used
to stop the motion at the instant of droplet contact; no appre-
ciable shrinkage due to evaporation takes place and accurate
calibration data is obtained.  The duration of the flash is ap-
proximately one microsecond, which is compatible with movement
and shrinkage of the droplet in the diameter range of interest.
Simultaneously, the electrical signal from the probe is displayed
on an oscilloscope and photographed.  These two photographic
records provide the data for calibrating the DC-2.

     With such equipment, the attachment mechanisms of droplets
can be comprehensively studied.  In this manner, the effects
of surface tension between the droplet and the wire have been
investigated.  Further, the influence of eccentric collision2
between the droplet and the wire was studied as a function of
droplet size and velocity relative to the wire.  Also the limita-
tions on flow velocity were investigated3 and an upper bound
on the droplet size was designed for a flow velocity of approxi-
mately 10 m per second for droplets no larger than 600 urn.  If
higher flow velocities are encountered, the large droplets tend
to shatter upon contact with the wire.

     Using the above-mentioned equipment, a complete calibration
curve has also been developed for the DC-2 and this calibration
curve has been implemented into the electronics of the system.
The calibration curve provides a direct relationship between
the droplet size and the electronic signal generated by the
probe, as droplets interact at low velocities.  Under actual
field conditions, the flow influences the droplets interacting
with the wire.  This type of flow phenomena is usually expressed
in terms of a capture area which is a relationship dependent
upon droplet size.  Such problems have been investigated in
aerosol filtration **'5 using a two-dimensional analysis for the
flow past an infinite cylinder.  It can be shown that viscous
conditions have a significant effect upon the capture area for
small droplets.  These effects are most important in the size
range from 1 ym to 10 ym.


                               308

-------
     To further verify the performance of  the DC-2,  a  series
of laboratory tests were performed to validate  the device  with
other apparatus such as the Brink impactor which  is  used  to
sample droplet and particulate distributions in industrial ap-
plications.  To minimize any measurement error,  a closed  system
with a steady flow was used in the laboratory  (Figure  4).   The
droplets were generated using a disc rotating at  a constant speed
in a closed box.  The entrained droplets were drawn  from  the
box by a constant volume pump (0.03 ft3/min) located downstream
of the impactor and the flow was returned  to the  box.   During
the test, the droplet distributions upstream and  downstream of
the impactor were monitored by the DC-2s noted  as A  and B  in
Figure 4.

     The system was operated with pure water or  a 10%  sodium
chloride solution.  Aluminum foil cups were used  as  targets in
the impactor.  The tests with pure water identified  some  sources
of measurement errors in the impactor.  For example, the DC-2
at location A indicated a stable droplet distribution,  but the
impactor results were erratic.  The length of the sampling time
has a pronounced influence on the measurements  with  the impactor
and the scatter of data was found to be unacceptable.   These
problems were attributed to evaporation and/or  condensation taking
place at various points in the impactor.  Because of these prob-
lems with the impactor, the quantitative studies with  pure water
were discontinued early in the research.
                             FLOW
                      MANOMETER
                      Figure 4. Laboratory apparatus.
                               309

-------
     The impactor measurements with a salt solution were more
dependable, but not entirely satisfactory.  Again, the impactor
results tended to have excessive scatter which was more pronounced
as the sampling time increased.  By very careful measurement,
it was determined that the salt concentration of the liquid col-
lected at the impact target is less than 10% and often as low
as 5%.  This result suggests that the samples were being diluted
by condensation of water vapor from the saturated flow.  Another
interesting observation from the impactor studies was demonstrated
by the transient behavior at its output.  The droplet concentra-
tion measured by the DC-2 at location B was initially very low.
Approximately 10 to 60 minutes (depending on the number of impac-
tor stages) were required for the droplet distribution to sta-
bilize and to establish a meaningful distribution.  Hence, the
impactor must be conditioned to the sampled environment to achieve
reliable data.

     All subsequent tests were carefully designed to permit ade-
quate time for the impactor to stabilize, but the impactor data
still exhibited some scatter.  In an attempt to further improve
performance, the impactor was placed inside the box where the
droplets are generated.  After "soaking" in the test environ-
ment, tests were performed, but only minor improvements in the
performance of the impactor were observed.

     Based upon this experience with the impactor, some carefully
selected and controlled tests were performed to provide data
for comparing the DC-2 and the impactor.  A typical distribu-
tion of number concentration versus droplet diameter is shown
in Figure 5.  The results from the DC-2 are presented as the
dashed curve and include the effects of the flow field on the
capture size of the wire.  The results from the impactor are
rather close considering the scatter associated with such mea-
surements .

     Another series of tests currently in progress utilizes a
well-calibrated spray nozzle in an open system.  The nozzle pro-
duces a very high concentration of droplets in the size range
from 1 urn to 50 urn.  A very carefully controlled uniform flow
condition is established with this system and the flow is con-
fined to a tube approximately 1 inch in diameter.  Steady state
conditions are readily established with this system and the mass
flow is determined at a specified operating pressure by direct
measurement of the consumed liquid.  In this manner the entrained
mass measured with the DC-2 can be directly compared with the
fluid flow through the nozzle.  These tests are currently in
progress and initial results indicate a favorable comparison.
                               310

-------
FIELD/LABORATORY EQUIPMENT

     The basic equipment for measurements  in the field and the
laboratory consists of the probe  and  the DC-2 electronic box.
The droplet distribution data  acquired  during each sample period
can be manually read via the liquid crystal display and the
results recorded on appropriate log sheets.  To facilitate the
collection of many data samples,  a printer/controller unit was
developed for controlling two  DC-2s.  The  unit is useful when
simultaneous measurements are  required  upstream and downstream
of a device  (e.g., to evaluate the efficiency of a demister).
A schematic configuration of the  equipment is shown in Figure 6.

     Both DC-2 units, A and B, are under  the direct control of
the printer/controller.  Samples  can  be taken in a continuous
mode with the data from units  A and B printed after the comple-
tion of each data cycle.  The  system  can  also be used for periodic
sampling with units A and B.   The time  period can be preset to
5, 10, 15, 30, 60 or 120 minutes  by the operator.  In either
mode, the printed data includes all the measured parameters and
the real-time when the data cycle was completed.  After complet-
ing a specified number of data cycles,  the printer/controller
automatically terminates operation.
10°
— ^
E
3.
M
0
— ' 104
Q~
I
r—
o"
e io3
D
aC
E
^_
LI
J
5 1Q2
J
c
LI
D
E
^
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Z
101,
	 — . IMPACTOR
	 DC-2 DATA WITH FLOW
Ij FIELD CORRECTION
V
" \
\
\\
\\
\ \
\\
\\
\ x
\ x^
X \
X ^
v ^N.
X * \^

N^ »^
x ^>.
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t r • j
  4      6

DIAMETER D, jum
                                                   10
         Figure 5. Number concentrations for the DC-2 and impactor. Impactor
               sample period equals 80 min.
                                311

-------
     More recently, KLD  has  interfaced the DC-2 with a micro-
processor system to further  facilitate the acquisition of a  large
number of data sample  points.   This type of arrangement has  been
very advantageous during the laboratory tests where hundreds
of data samples are recorded and must be subsequently processed
to analyze the results.   The printer and computer for this system
are too large and bulky  for  application to field work.  However,
KLD has recently designed a  compact microprocessor system which
is capable of data acquisition and analysis in the field environ-
ment.

     For application  in  the  field, devices to support the probe
while surveying across large ducts are available.  Currently
a telescoping pole approximately 2 in. in diameter is used to
survey across a large  duct in typical power plant applications.
The pole is capable of extending to 14 feet.  The pole itself
is supported by a support bearing attached to the sidewall of
the duct.  This type  of  equipment reduces the data activities
in the field to a routine procedure after the appropriate access
ports have been installed.
                    PROBE


                    A
                DC-2
                                     o
                                      o
                                         PRINTER/CONTROLLER
                DC-2
                     PROBE
              Figure 6. Printer/controller for automatic operation with two
                    DC-2 units.
                                312

-------
FIELD MEASUREMENTS

     The measurement of droplet distributions and concentrations
is important in several applications such as the evaluation of
demister performance in power plants, assessment of entrained
mass in quenching towers and environmental control  in  large manu-
facturing complexes where oil mist can be a problem.   Some of
these studies  have been documented in other reports.

     The field studies at the limestone scrubber/demisters pro-
vided the most severe test environment because of the  accumu-
lation of limestone on the sensor.  However, the contamination
of the sensor is easily detected as a reduction of  the droplet
counting rate or by periodically inspecting the sensor.  Then
the contaminated sensor is cleaned with hydrochloric acid or
the entire probe is replaced to expedite the work.

     Field studies of limestone scrubber/demister have been per-
formed at power plants at Shippingport, PA and Becker, MN.  At
Shippingport a 12-foot square section was surveyed  through six
ports approximately 40 feet downstream of the demister stage.
At one site, the tests were performed downstream of a  single
demister.  At the second site, two demisters were in series and
measurements were taken after the second demister.  For both
sites the duct downstream of the demister is horizontal.  Such
a survey required about two hours to complete following equip-
ment set-up.  A total of 51 droplet distributions were recorded.

     The average velocity measured with the DC-2 was 10 m/sec,
and this value was used for computing the number concentration.
Typical results are shown in Figure 7 as a function of droplet
size.  The upper curve is the number distribution for  the site
with a single demister, whereas the lower curve is  for the double
demisters in series.

     The data for the two sites is summarized below:

                                              Number of Demisters
                                                1             2
Volume concentration (gr/ft )                 0.21          0.093
Droplet concentration (no./cm3)                525           301
Mass mean diameter (urn)                        11.9          11.0

     At the Becker Power Plant the mass carry-over  from the de-
mister section was determined.  In this power plant the demisters
and duct work have a vertical orientation and the surveys were
performed over a cross-section of approximately 15  x 21 ft.
Five access ports were located along each of the longest sides
of the duct.  The surveys were performed by extending a pole
approximately half-way into the duct and taking measurements
from the mid-point of the duct to the wall.   A total of 30 spatial
locations were used over the entire cross-section.  At each loca-
tion two to four measurements were taken and averaged  to obtain
the distribution at each location.


                               313

-------
     A demister  with two rows of chevrons  is  used in this power
plant.  During  this evaluation period, one row of chevrons was
removed and  the  tests repeated to assess the  effect on the mass
carry-over.   The size of this coal power plant is 760 megawatts.
The scrubbers remove approximately 80% of  the sulfur dioxide
and the liquid  to gas ratio is 30 gallons/1000 ft3.

CONCLUSIONS

     The hot-wire sensor is an effective means of measuring the
droplet size  and concentration.  The DC-2  has been successfully
used in the  laboratory and has provided valuable insight into
the behavior  and performance of impactors  when used as a sampling
device for droplet distributions.  Also, the  DC-2 has been demon-
strated in the  field under various adverse environments.  The
field studies were successful and useful measurements were ob-
tained.  Measurements can be taken rapidly with a minimum of
labor and set-up time.
         cc
         I-
         LLJ
         u
         z
         o
         o
         DC
         LU
         DQ
         2
         13
         z
              103
              10°
             10'
10
 -2
10
 ,-3
             10'=
             10
               -6
                            	 SINGLE DEMISTER SECTION
                            	DOUBLE DEMISTER SECTION
                              i	
                                              i	
                            10           100

                            DROP DIAMETER D, urn
                                        1000
           Figure 7. Number concentration vs. droplet diameter for a single and
                  double demister.
                                314

-------
ACKNOWLEDGEMENTS

     The research and development work on hot wire technology
for the detection and measurement of droplets was sponsored by the
Environmental Protection Agency, Research Triangle Park, NC.
Mr. Bruce Harris was the Project Officer for the EPA and his
support and suggestions are gratefully acknowledged.  The mea-
surements at Shippingport were coordinated by Mr. Dennis Martin
of York Research.  The measurements at the Becker Power Plant
were sponsored by Combustion Engineering, Inc. and were under
the supervision of Mr. Kal Malki.

REFERENCES

1.   Medecki,  H., K. Wu, and D.E. Magnus.  Development of Droplet
     Sizing Technique for the Evaluation of Scrubbing Systems.
     EPA-600/7-79-166, U.S. Environmental Protection Agency,
     Research Triangle Park, NC, July 1979.

2.   Medecki,  H., M. Kaufman, and D.E. Magnus.  Design, Develop-
     ment, and Field Test of a Droplet Measuring Device.  Environ-
     mental Protection Technology Series.  EPA-650/2-75-018,
     U.S. Environmental Protection Agency, Research Triangle
     Park, NC, February 1975.

3.   Medecki,  H. and D. Magnus.  Liquid Aerosol Detection and
     Measurement.  Presented at 68th Annual Meeting of the Air
     Pollution Control Association, 1975.

4.   Davies, C.N.,  ed.  Aerosol Science.  Academic Press, New
     York, j.966.

5.   Fuchs, N.A.  The Mechanics of Aerosols.   Pergamon Press,
     New York, 1964.
                               315

-------
                             PAPER 18


     SOME  AERODYNAMIC  METHODS  FOR SAMPLING INHALABLE PARTICLES
                         WALLACE B. SMITH
                        KENNETH M. GUSHING
                        14.  CHRISTINE  THOMAS
                       RUFUS R. WILSON, JR.
                   SOUTHERN  RESEARCH INSTITUTE

                                AND

                          D.  BRUCE HARRIS
         INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY-RTF
               U.S. ENVIRONMENTAL PROTECTION AGENCY

INTRODUCTION

     At present, most measurements used to characterize particulate
emissions from stationary sources are made with cascade impactors,
cyclone trains, and filters.  However, these methods do not dis-
tinguish between the inhalable and non-inhalable fractions of
the suspended particles.  The objective of the investigation
described in this paper was the development of equipment and
procedures for measuring the concentration of inhalable particles,
either by modifying existing sampling systems and procedures
or by developing new ones.  The systems that were developed are
to bs used for establishing emission factors for stationary
sources by measuring the concentrations of inhalable particles
in stacks and in fugitive emissions.  The systems were designed
to have a second cut point at 2.5 ± 0.5 urn aerodynamic diameter.
This requirement ensures that the systems used to measure the
emission factors will yield data comparable to that measured
in the ambient atmosphere using the EPA dichotomous samplers.

     The devices considered as candidates for inhalable particulate
samplers were impactors, cyclones, and horizontal elutriators.

     Impactors are compact and the theory describing their opera-
tion is well developed.  However, impactors of conventional de-
signs are inefficient collectors for particles with diameters
larger than the cut point values of the impactor stages.1-3
Particle bounce resulting in reentrainment is evidently respon-
sible for much of the inefficiency.
                               316

-------
     Cyclone collectors are not subject to this problem, and
they also have the advantage that the inlet is at a right angle
to the axis of the cyclone and hence the sampling nozzle can
be pointed directly into the gas stream in the stack without
the need for a button-hook or curved nozzle.  On the other hand,
cyclone samplers are bulky compared to other samplers, and no
adequate theory exists for their performance.

     Horizontal elutriators are also somewhat bulky and they
are sensitive to orientation.  However, reentrainment is not
a problem, and the theory describing their performance is straight-
forward and accurate.1*

     Four prototype systems were investigated during this study:
(1) horizontal elutriators for sampling fugitive emissions and
to be used as precollectors for in-stack cascade impactors and
the EPA Source Assessment Sampling System  (SASS),  (2) a high-
volume cascade impactor for fugitive emissions, (3) a precollec-
tor cyclone for use with in-stack cascade  impactors, and  (4)
a dual-cyclone train for in-stack sampling.  All of the prototype
systems were evaluated under conditions of gas flow and tempera-
ture consistent with those present in actual sampling conditions.

EXPERIMENTAL INVESTIGATION AND RESULTS

     Prototype systems employing horizontal elutriators, inertial
impactors, and cyclones were fabricated and tested in the labora-
tory.

Horizontal Elutriators

     Horizontal elutriators have consistently predictable col-
lection efficiencies, as confirmed by Stein, et al.,5 Rimberg
and Thomas,6 and Corn, et al.7  Elutriators have been used both
as particle sizing instruments and as particle collection de-
vices . 8

     The experiments described in this section were performed
to verify the theory of particle collection by settling and to
develop design criteria for inlet collectors to be used in con-
junction with two sampling systems developed for the Environ-
mental Protection Agency: the Fugitive Ambient Sampling Train
(FAST)  and the Source Assessment Sampling  System (SASS).  Designs
were also developed for applications with  in-stack cascade im-
pactors.

     The initial concept of the horizontal elutriator was the
result of studies to measure quantitatively the deposition of
aerosol particles on surfaces adjacent to, or suspended in, mov-
ing gas streams flowing through laboratory apparatus.  Natanson1*
                               317

-------
and Thomas6 independently solved this problem theoretically  for
a circular horizontal tube of radius a.  Although the deriva-
tions are somewhat complex, the results can be summarized  and
simplified in terms of the collection efficiency  (Eff) by  the
following equation:


   Eff = f [2e Vl - £2/3 - £1/3 Vl - £2/3 + arcsin  e1/3]       (1)


where
           3V L
             s
       £   8aV
       V  is the settling velocity,
        S

        L is the length of tube,

        a is the radius of tube, and

        V is the average velocity of the gas.

     The theory describing the performance of a  rectangular  flat
plate elutriator is considerably less complex and is  re-derived
here to give the reader a better understanding of the particle
motion in the elutriator.  The settling velocity  of spheres  in
a gas stream is given by the equation
where

       V   is  the  settling  velocity,
        o

        g  is  the  acceleration due  to  gravity,

        C  is  the  slip  correction factor,

        p  is  the  particle  density,

        d  is  the  particle  diameter, and

        Vi  is  the  viscosity of the  gas.

     In health-related studies,  the aerodynamic behavior of  the
particles is of interest.   It is therefore convenient to relate
the settling velocity of all particles, whatever their shape
or density, to that of spheres having unit density.  The aero-
dynamic diameter  is defined as the diameter of a unit density
sphere having the same settling velocity as the particle of
interest.   The aerodynamic  diameter is given from Equation 2
by setting p = 1 g/cm3 (the units must be retained) .  Also,  for
                               318

-------
particles larger  than about  2 ym, the slip correction factor
is approximately  equal to  unity.  A graph of settling velocity
vs. diameter is shown in Figure 1.

     For fully developed flow between parallel plates, the velocity
profile of a gas  is  parabolic with the maximum velocity equal
to 1.5 times the  average and with zero velocity at the plates:
where

       V  is the  velocity parallel to the plates, at a point y,
        A

       y is the displacement  above the bottom plate,

       h is the spacing  between plates, and

       V is the average  velocity of the gas.

     The velocity profile and a typical particle trajectory are
illustrated in Figure  2.

     The efficiency with which particles are collected is deter-
mined by the dimensions  of  the channel, the velocity of the gas,
the settling velocity  of the  particles, and the height at which
the particles enter the  channel.

     Consider a particle which enters the channel at position
y0 as shown in Figure  3  and which has a trajectory of length
L (the length of  the channel) .  All particles of this diameter
or larger entering at  or below position y  will be captured.
All particles of  this  diameter entering the channel at positions
higher than yQ will penetrate the channel.

     Now, from Equation  3:
       at ~Vh  " h2  /  v

but dy is given  by dy = -V dt; therefore
                         s
      jf-'-UVr)*'
'0      vs  "y
           *o
                                                             (4)
                              319

-------
I
I  0,
Ul
LLJ
V)
   0.01
  0.001
              0.6     1        2       4       8 10      20      40

                  AERODYNAMIC PARTICLE DIAMETER, urn     4181-86



        Figure 1.  Settling velocity in air for unit density spheres.
                                  320

-------
   v>
                             V
    X
\ .
o
                                                                   4181-106
2. Velocity profile and particle trajectory between parallel plates.
             Figure 3. Zone of 100% particle collection.
                                                                        4181-73
                           321

-------
from which the settling velocity of the particle may be deter-
mined.

     If the particles are uniformly distributed within the gas,
the fractional collection efficiency of the particle illustrated
in Figure 2 is equal to the ratio of the volume of gas passing
below position yo  to the total volume; thus:
       Eff. =
               •/
                •fr\
dy
where W is the width of the channel.

     Now, from Equation 4,


       Eff. . V . CE^
              h v   18 Mh V

     The theoretical efficiency curves for a horizontal elutriator
with a circular cross-section  (from Equation 1) and for a hori-
zontal elutriator with a rectangular cross-section  (from Equa-
tion 5), both designed to have a cut point of 15 ym aerodynamic
diameter, are shown for comparison in Figure 4.

     The efficiency is found to be independent of the  vertical
velocity profile and, as Fuchs1* observed, Equation  5 can be
derived more easily assuming plug flow.

Experimental Procedures—

     Experiments were conducted to verify Equation 5 and to set
design parameters for the FAST and SASS inlets.

     Figure 5 is a schematic diagram of the experimental apparatus
used to investigate the performance of a horizontal elutriator
designed to have a cut point (D50)  of 15 um aerodynamic diameter.
The settling chamber consists of 28 channels, each 7 mm high,
17.8 cm wide, and 38.1 or 20 cm long.  A high volume blower
(Model 305, Sierra Instruments) connected in series with a vari-
able voltage transformer was used to supply the desired air flow
rate through the chamber.  Monodisperse particles of methylene
blue were generated using a vibrating orifice aerosol generator
(VOAG)  for particles larger than 4 ym aerodynamic diameter.
During each test, the particles were sampled and checked fre-
quently by optical microscopy to ensure constant monodispersity.
                               322

-------
All particles  entering the horizontal elutriator were collected
either  by  settling on the plates  or  on the 8 in. x 10 in.  (20.3
cm x  25.4  cm)  filter downstream from the plates.

      Upon  completion of each test, the plates and filter were
washed  separately with tap water.  Samples from each wash  were
centrifuged  to remove debris, and the masses of methylene  blue
collected  on the plates and on the filter were determined  by
absorption spectroscopy.

      The velocity distribution through the settling chamber  was
studied to determine the configuration necessary to obtain uni-
form  flow.   The use of two filters and an extended flared  inlet
was necessary  to provide the desired velocity distribution.
Figure  6 is  a  velocity profile measured using a thermal anemom-
eter  immediately upstream from the blower before the plates  were
in position.   From these data, it was evident that the blower
was pulling  uniformly across the  rectangular opening where the
20.3  cm x  25.4 cm filter was positioned.   Figure 7 shows the
velocity profile measured upstream of the collector plates.
  u
  •z.
  HI
  o
  LLJ
  O
  UJ
  O
  O
                       RECTANGULAR
                       CIRCULAR
    1.
      1.0      2.0      4.0   6.0  8.0 10     20       40    60  80 100

                   GEOMETRIC MEAN DIAMETER, micrometers      4181-126
      Figure 4.  Theoretical collection efficiency by particle settling in rectangular
             and circular tubes.
                                323

-------
U>
ro
*»
                        COMPRESSED AIR LINE
                                  REGULATOR
                                  AND TRAP

                                  REGULATOR
                                  DRYER
                            FLARED INLET
                                                    no.
                                  ABSOLUTE FILTER
REGULATOR
   VALVE
                                          VIBRATING

                                          AEROSOL
                                          GENERATOR
                           ROTAMETERS_D.SPERSIpNAIR
I
                                  DISPERSION AIR
                                                                                      FILTER
                                                                  SETTLING CHAMBER
                                                                                     VARIABLE
                                                                                     VOLTAGE
                                                                                     TRANSFORMER
                                                                  HIGH VOLUME
                                                                  AIR SAMPLER
                                                                           I
                                                                       SYRINGE PUMP                WATER MANOMETER
                                                                                    FUNCTION GENERATOR
                                                                                                           4181-74
                                 Figure 5. Apparatus used to measure the collection efficiency of the settling chamber.

-------
      The velocity profiles shown  in Figures 6 and  7 were  con-
sidered satisfactory,  and the overall average velocity was  used
to calculate  the theoretical performance  curves  for the system.
The  average velocity through the  chamber,  measured using  the
thermal anemometer, was  in agreement with previous calibration
of the blower.
                               /

V (m/sec)

  0.30

  0.20

  0.10
STATISTICAL DATA:
  MEAN, x , = 0.24 m/sec
STANDARD DEVIATION,
  Sx = 0.02 m/sec
COEFFICIENT OF VARIATION,
  SX/JT = 8.2%
                                                                   4181-107
       Figure 6. Profile of the air velocity immediately upstream from the
              blower of the sett/ing chamber before the plates were positioned.
                                  325

-------
                                                 STATISTICAL DATA:
                                                   MEAN, x , = 0.23 m/sec
                                                 STANDARD DEVIATION,
                                                   Sx = 0.02 m/sec
                                                 COEFFICIENT OF VARIATION,
                                                   Sx/x = 8.8%
                                                                  4181-108
              Figure 7. Profile of the air velocity upstream from the plates
                     of the settling chamber.
Results—

     Two sets of experimental data were obtained from  the testing
of the horizontal  elutriator.   The first set  was acquired while
operating the settling chamber  at an average  gas velocity of
70 cm/sec and a plate length of 38.1 cm.   The second data set
was obtained by operating the system at 40 cm/sec after  shorten-
ing the  plate length to 20 cm.   The theoretical curves of the
                                  326

-------
collection efficiency versus aerodynamic particle diameter  shown
in Figures 8 and 9  were developed  from Equation 5 using  the
following parameter  values:
     Figure 8

     p  =  1.35 g/cm3

     g  =  9.8 m/sec2

     L  =  38.1 cm

     y  =  181 micropoise

     h  =  0.701 cm

     V  =  70 cm/sec

     Reynolds No. =  315
Figure  9

p = 1.35  g/cm3

g = 9.8 m/sec2

L = 20  cm

p = 181 micropoise

h = 0.701 cm

V = 40  cm/sec

Reynolds  No. = 180
     The calculated  values from  theory for  the collection effi-
ciency  were found  to be in excellent agreement with the  measured
values.   No corrections were made  for end effects.
    u
    z
    UJ
    UJ
    O
    U
                 2    34    6   8 10      20   30  40

                    AERODYNAMIC PARTICLE DIAMETER, Mm
             60  80 100
                4181-109
  Figure 8. Theoretical and experimental collection efficiencies for a horizontal elutriator
         with rectangular cross-section, plate length 38.1 cm, average gas velocity 70 cm/sec.
                                 327

-------
Collector Design—

     The experiments described above  indicated that the  theo-
retical equations can be used to predict particle collection
by horizontal  elutriators to a high degree of accuracy.  Con-
sequently,  the equations were used to create design nomographs
for inhalable  particulate precollectors  to be used in conjunction
with the three systems of interest.   Design parameters were
calculated  for horizontal elutriators to be used with:   (1) cas-
cade impactors operated at 14.2 Jl/min   and 149°C, (2) SASS
trains operated at 185 £/min  and 204°C, and (3) FAST trains
operated at 5,282 Jl/min  and 23°C.

     Figures 10, 11, and 12 are the design nomographs for  the
three trains.   On the vertical axis is the open area required,
neglecting  the thickness of the tube  walls.  The horizontal axis
is the length  of the elutriator required to yield the inhal-
able particulate performance at the specified flow rate  and tem-
perature.   In  constructing the graphs, it is assumed that  the
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1 2 3 4 6 8 10 20 40 60 80 100
AERODYNAMIC PARTICLE DIAMETER, Aim 4181-75
   Figure 9. Theoretical and experimental collection efficiencies for a horizontal elutriator
          with rectangular cross-section, plate length 20 cm, average gas velocity 40 cm/sec.
                                328

-------
10
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                   RECTANGULAR ELUTRIATOR
                 2       3     45678
                        PLATE SEPARATION, mm
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                            RECTANGULAR ELUTRIATOR
                                                                           CYLINDRICAL ELUTRIATOR
                       TUBE DIAMETER, mm
              1.0
2.0
3,0    4.0   5.0  6   7  8  9 10

                      LENGTH, cm
                                                                                      30     40
50  60 70

  4181-124
                             Figure 10.  Relationship of design parameters for horizontal elutriators with
                                        DSQ cutpoints of 15 fim aerodynamic diameter used as precollectors
                                        for instack cascade impactors.

-------
rectangular channels  have widths much greater  than their heights,
so that  the vertical  walls will not  have a significant effect
on the gas flow.

      It  can be seen  from these graphs that circular tubes can
be used  to construct  a system having the required performance
with  much smaller overall dimensions than rectangular tubes  or
channels.
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4181-123
          Figure 11.  Relationship of design parameters for horizontal elutriators with
                   050 outpoints of 15 jum aerodynamic diameter to be used with
                   SASS trains.
                                 330

-------
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                                                                                        4181-125
           Figure  12.  Relationship of design parameters for horizontal elutriators with
                      DSQ outpoints of 15 tim aerodynamic diameter to be used with
                      FAST.

-------
High-Volume Impactor

     The theory of particle collection by impaction has been
developed to a state in which the efficiency can be reasonably
well predicted for ideal conditions if the geometry of the system
is known.9'10  Critical dimensions and parameters of the system
are the jet width, the length of the jet, the jet-plate spacing,
the jet velocity, the Reynolds number of the jet, and the type
of particle collection surface.  In addition to being a well-
understood system of particle separation and sizing, impactors
are very compact in size.

     However, impactors can suffer from a severe limitation if
the particles or substrates are not adhesive.  Particles much
larger than the D50 have greater stopping distances and may
strike the substrates with high velocities and rebound.  This
phenomenon results in an efficiency curve that rises with par-
ticle diameter to a maximum, frequently at less than 70-80 per-
cent, and then declines to much lower efficiencies for still
larger particles.1'2'3

Experimental Procedures—

     A prototype impactor was constructed using six first stages
from a commercially available cascade impactor (Model 35, Sierra
Instruments) in parallel.  The impactor is designed to operate
at a flow rate of about 0.020 m3/sec.  In this study, which was
performed before the inhalable particulate performance curve
was developed, the flow rate through each impactor was approxi-
mately 0.015 m3/sec.  The reduced flow rate was selected to
achieve 95 percent collection of 15-um particles.  The impactor
stages were covered either with glass fiber substrates or grease.

     The FAST including the prototype impactor stage is shown
schematically in Figure 13.  The calibration aerosols were gene-
rated using a vibrating orifice aerosol generator as described
above.  For these tests, however, ammonium fluorescein particles
were used and the cleanup procedure was slightly different.
To help ensure the recovery of the aerosol particles trapped
by the grease (petroleum jelly) on the impactor collection plates,
they were washed with benzene in an ultrasonic cleaner in addi-
tion to being washed with ammonium hydroxide.  Glass fiber sub-
strates were washed with ammonium hydroxide.

     As before, the mass of material collected on each surface
was determined by absorption spectroscopy.

Results—

     The results of a limited calibration study are shown in
Figure 14.  It can be seen that particle bounce is severe with
                               332

-------
           INLET
           THERMOCOUPLE
                       CYCLONE
                                  FILTER
    INLET
                        CYCLONE
                             TRAP
                             OUTLET
                             THERMOCOUPLE
                    VACUUM
                    PUMP
                     EXHAUST

                      4181-95
             Figure 13.  Fugitive air sampling train (FAST) components.
both glass  fiber  and  greased substrates.  Because of  these un-
satisfactory  results,  the experiments with impactors  were aban-
doned in favor of  the horizontal elutriator.  It should  be noted
that stages 2-5 of the same type of impactor have been calibrated
by Willeke  and shown  to behave well with liquid particles.11

Cyclones

     Although the  flow in cyclones is more complicated than
in impactors  and  no theory exists to adequately predict  their
behavior, several  experimental investigations have  been  performed
demonstrating their utility for separating and sizing small par-
ticles. 1 2 ': 3'x **   Smith et al.,15 and John et al.,16 have demon-
strated that  the  curves of particle collection efficiency for
small cyclones can be as steep as those of impactors, and signi-
ficant  reentrainment  does not occur.  Chan and Lippmann17 have
shown that  experimental efficiency data for small cyclones can
be fitted well using  the empirical relationship:
       Eff = 0.5  +  0.5  tanh
+  A-2B
(6)
where
        Q is  the  sample flow rate, cm3/sec,
                                333

-------
       D   is the diameter of  the sampled  particle,  cm, and



       A,B,K,n are  empirical  constants.



     Also it was shown that the D50 vs.  flow rate  relationship

is given  over a limited range of sampling conditions by:
        D50 = KQ
                n
         (7)
          100
           90
           80
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                     AERODYNAMIC PARTICLE DIAMETER, jum
20
                                                        4100-13

              Figure 14. Particle collection efficiency for the impactor.
                                   334

-------
     From their own research and data reported by others, Chan
and Lippmann reported values of K ranging from 6.17 to 4591,
and values of n from -0.636 to -2.13.  Smith et al. reported
values of K from 14.0 to 44.6, and n from -0.63 to -1.11.  Al-
though the trend in the data is for n to have larger values for
small cyclones (D50's) and K to be larger, the correlation is
not consistent enough to be predicted from the cyclone geometry,
and no data are reported for temperatures other than ambient.
Furthermore, there are definite discontinuities and hysteresis
effects in the relationship given in Equation 7, even for indivi-
dual cyclones, as the flow is increased and decreased.  The dis-
continuous and hysteresis effects are generally attributed to
transitions from turbulent to laminar flow, or the reverse, in
the outlet tube of the cyclone as the flow is changed.13

     Smith et al. found the D50 of cyclones to increase linearly
as the gas temperature and viscosity were increased; but again
the rate of increase was not predictable from the cyclone geometry.
Certainly a modification to Equation 7 would be required to pre-
dict any temperature dependence.  Lacking an adequate theory
for predicting the performance of cyclones before they are de-
signed and calibrated, it was found necessary in this study,
as in previous work, to extrapolate the dimensions for a new
cyclone to give the desired performance from those of similar
cyclones of known performance.

     However, because of these difficulties, and the requirement
that the inhalable particulate cyclones always be operated to
yield D50's at 15 ± 2 urn, it was still considered necessary to
calibrate them over a range of temperatures and flow rates similar
to those expected in field operation.

Experimental Procedures—

     The objective of this phase of the program to develop sam-
plers for inhalable particles was to design and evaluate two
systems:  (1) a cyclone to be used as the precollector for cas-
cade impactors, and (2) a system, consisting of two cyclones
and a filter in series, to be used as the primary system for
measuring the total particulate concentration, the inhalable
particulate concentration, and the fine particle concentration.
Both systems are to be used in process streams where the particle
concentration and temperature are generally much higher than
in the atmosphere.  The precollector for impactors and the first
cyclone in the series train must have efficiency curves satis-
fying the specifications for inhalable particulate samplers shown
in Figure 4.  The second cyclone in the series train must be
designed to have a D50 of 2.5 ± 0.5 ym aerodynamic.

     The nominal operating conditions used in designing the
systems were flow rates of 14 &/min  and 21 Jl/min  at 150°C,
respectively, for the precollector and cyclone systems.  With
                               335

-------
these operating conditions  as  a goal,  the dimensions of the
cyclones were extrapolated  from those  previously evaluated.15

     Figures 15 and 16 are  schematic  illustrations of the two
new systems.  The precollector cyclone is designated SRI-IX and
the large cyclone in  the  series train, SRI-X.   Cyclone SRI-III,
which had been previously evaluated as part of the SRI/EPA 5-
stage cyclone train,  was  found to  be  adequate  for the smaller
cyclone in the new system.

     The critical dimensions of all three cyclones are given
in Figure 17.

     In order to calibrate  the cyclones at elevated temperatures,
the heating arrangement shown  in Figure 18 was used in conjunc-
tion with the vibrating orifice aerosol generator described above.
Tests were made at temperatures of 23°C, 93°C, and 150°C.  Am-
monium fluorescein particles were  used for calibrating the cyc-
lones.  Samples were  taken  frequently  of the heated aerosol to
ensure that the calibration system was stable  and that the par-
ticles were spherical and of the proper size.

     In this study, the primary objective was  to determine the
operating conditions  under  which  the  cyclones  satisfied the de-
sign criteria.  For this  purpose,  it  was sufficient to use an
abbreviated calibration procedure  and  thus to reduce the exten-
sive amount of testing that would  be  needed for complete calibra-
tion.  At a specific  temperature,  monodisperse particles having
nominal aerodynamic diameters  of  15 urn were generated and sam-
pled.  Tests were made at a variety of flow rates to determine
the sampling rate required  to  yield a D50 of 15 ym at the given
temperature.  Only limited  data were  taken to determine collec-
tion efficiency vs. particle diameter.
                             SAMPLING NOZZLE
               CYCLONE
               D50 = 15 ± 2 ;um
CASCADE IMPACTOR
                                                         PROBE
                  4181-76
        Figure 15. Schematic of a cascade impactor/precollector cyclone system.
                                336

-------
     When preparing to generate  monodisperse particles using
the vibrating orifice method,  it is  necessary to know the solu-
tion flow rate and frequency of  vibration in order to calculate
the concentration of solute required to yield the desired par-
ticle diameter after drying.   In practice,  the flow rate can
be selected and the solution prepared precisely, but the fre-
quency at which the generator  is finally found to yield maximum
stability is unpredictable to  some extent.   Therefore, as indi-
cated in the figure captions,  the actual particle diameters dif-
fered slightly from 15 urn.  In these tests  the particles had
aerodynamic diameters of  15.0  ±  0.6  jam.

Results—

     Figures 19-22 show the calibration data for the three cyclones,
In Figure 19, the particle collection efficiency is plotted vs.
flow rate for cyclone SRI-IX.

     As indicated in the  figure, data were  taken at 23°C, 93°C,
and 150°C.  Similar data  are shown in Figure 20 for cyclone SRI-X.


     The settling velocity in  air of 15 ym  particles is 0.7 cm/sec
and there was some concern that  settling might influence the
collection efficiency of  the larger  cyclones by making them sensi-
tive to orientation.  In  Figure  20,  which contains calibration
data for cyclone SRI-X, data are shown taken with the cyclone
in both vertical and horizontal  orientations.  It can be seen
that there is little, if  any,  effect due to particle settling.
                                   SAMPLING NOZZLE
                                                 PROBE
                      CYCLONE SRI-IX
                      D50 = 15 +2 f*"1
CYCLONE SRI III
D50 = 2.5 ± 0.6 Hm
                                                 4181-120
                Figure 16.  Schematic of two-cyclone system.
                                337

-------
                       T
                       i
               -H  B
                                1cup
                 D
                   cup"
       DIMENSIONS (CENTIMETERS)
CYCLONE
SRI-X
SRI-HI
SRI-IX
D
6.14
3.11
5.12
Din
1.83
0.75
1.53
De
2.17
0.83
1.81
B
2.92
0.76
2.43
H
8.47
4.91
7.06
h
2.82
1.40
2.35
Z
5.65
3.51
4.71
S
2.40
1.08
2.00
Hcup
2.635
2.22
2.26
Dcup
6.14
3.10
5.12
                                                       4181-22
Figure  17. Summary of cyclone dimensions.
                  338

-------
AEROSOL STREAM
FROM VIBRATING
ORIFICE AEROSOL
GENERATOR
IVBSOLUTE FILTER
                                    OVEN
                                   , KEPT AT
                                   I AEROSOL TEMPERATURE
                                               HEAT I
                                               EXCHANGER
                   SAMPLING
                   PORT
                                                   MERCURY   WATER
                                                   MANOMETER MANOMETER
                                                                4181-92

                 Figure 18. Calibration system for heated aerosols.


     The  data reported  in Figures 19 and 20 will be used to
select  the  flow rates of the  new sampling trains.   Since there
is no adequate theory for calculating cyclone  efficiency, cyclone
SRI-III was  calibrated  at the same flow rates  required for proper
operation of cyclone SRI-X.   These calibration data are shown
in Figure 21.  D50's and flow conditions for the three cyclones,
as derived  from the graphs, are:

     Cyclone SRI-III

     3.1  vim  (aerodynamic) D50 at 23°C, 11 S,/min

     2.6  urn  (aerodynamic) D50 at 93°C, 20 Jl/min

     2.3  ym  (aerodynamic) D50 at 150°C, 23 &/min

     Cyclone SRI-IX

     15 ym  (aerodynamic) D50  at  23°C, 6.8 5,/min

     15 ym  (aerodynamic) D50  at  93°C, 12 £/min

     15 ym  (aerodynamic) D50  at  150°C, 14 &/min
                                339

-------
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     Also,  limited data were taken with  particles with diameters
other than  15  ym using cyclone IX.  These  are shown plotted with
the inhalable  particulate performance  specifications in Figure  22.

     The data  reported above define the  operating points of
cyclones SRI-IX  and SRI-X at three discrete values of tempera-
ture.  Figure  23 shows the data plotted  on semi-log coordinates
with a smooth  line fitted to the points.   The equations of flow
rate vs. viscosity are:

     For cyclone SRI-X, Q =  (105 logy  -  225H/min
and for cyclone  SRI-IX, Q =  (69.5 logy - 150H/min.

     It is  not known at present how accurately these equations
can be extrapolated to temperatures greater than 150°C.

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FLOW RATE, £/min 4181-7S
        Figure 20.  Collection efficiency of cyclone X vs. flow rate for particles of
                 15±0.6 urn aerodynamic diameter.
                                341

-------
      In  order to gain a better  qualitative understanding of the
mechanisms  governing the performance of cyclones,  Table 1 was
prepared summarizing some of  the dimensions and  operating param-
eters  of cyclones evaluated at  Southern Research Institute.
The parameters of greatest  interest are the Stokes number of
15 pm particles in the inlet  and the ratio of  the  settling ve-
locity to the centripetal velocity of 15 ym particles in the
cyclone  body.  The latter is  calculated assuming that the air
flow  in  the cyclone body is a jet having the same  velocity and
diameter as in the inlet.   This is obviously a crude approxima-
tion,  but probably accurate enough to allow a  reasonable esti-
mate  of  the desired ratio.
              as

              u
              01
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              01
              Z
              O
              u
              01
              _i
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              u
                       AERODYNAMIC PARTICLE DIAMETER, jLtm
                                                   4181-87
          Figure 21. Collection efficiency vs. aerodynamic particle diameter for
                  Cyclone III at 22° and 11.3 Wmin (Q), 93°C and 19.8 l/min
                  (Q),and 150°C and 22.7 Z/min
                                 342

-------
     The settling  velocity Vs of unit  density spheres is given
by the expression  (equivalent to Equation 2):
       Vs = mgB
where
       m  is  the  particle mass,
       3  is  the  particle mobility, and
       g  is  the  acceleration due to gravity,

The centripetal  velocity VG is given  by:
\7  -
VC ~
            mV.
               ln
             R
       V
 in is the gas  velocity in the inlet  and
where

       R  is  the  cyclone radius.

The desired  ratio,  then, is:
       V
        s
                                                          (8)
                                                                 (9)
Vc
99
98
95
90
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Z
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£ 60
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                CYCLONE X
                Q = 105 log^ -225
                              CYCLONE IX
                              Q = 69.5 log/u -150
                        I
                                                 I
                   200           250        300

                       VISCOSITY (ju), micropoise
   400

4181-121
Figure 23. Gas flow rate versus viscosity at D^Q = 15
          diameter for cyclones IX andX.
                                                         aerodynamic
                                    344

-------
                             TABLE  1,   OPERATING PARAMETERS OF SRI CYCLONES
u>

Cyclone
Number
V
IV
III
II
I
BRINK
IX
X
Q (cm3/sec)
472
472
472
472
472
28
233(150°C)
190
D(cm)
1.52
2.54
3.11
3.66
4.47
1.27
5.11
6.14
D.
in
0.
0.
0.
1.
1.
0.
1.
1.
(cm)
30
57
75
01
27
51
53
83
Vin (cm/sec)
6670
2300
1100
600
370
130
130
70
Ap(mm H20)
1800
330
70
40
5
-
-
-
DSO
0.
0.
1.
2.
5.
13
15
15
(pm)
32
65
4
1
4



/St
0.1
0.1
0.1
0.1
0.2
0.6
0.3
0.2
gR/vin2
i.
2.
1.
5.
1.
4.


6 x 10"5
3 x 1C""
3 x 10"3
0 x 10~3
6 x 10"2
0 x 10~2
0.2
0.6

        Q  is  the sample flow rate
        D  is  the diameter  of the cyclone body
        Din  is  the diameter  of the  inlet
        Vj[n  is  the gas velocity in  the inlet
        AP is the pressure drop across the cyclone
        St  is  the Stokes  number of the 15-ym particles in the inlet
        gR/Vj_n  is the ratio  of the  settling velocity to the centripetal velocity in the cyclone
        body

-------
     The values of /St and VS/VC can be used to estimate whether
or not impaction onto the wall opposite the inlet or particle
settling is likely to play a_large part in the collection ef-
ficiency of a cyclone.  If /St is less than about 0.4, then
impaction is not likely to occur.10  If VS/VC is very small,
then settling is not likely to occur.  From Table 1, it can be
seen that impaction is probably very significant in the cyclone
used with the Brink impactor, while settling probably contri-
butes somewhat to the collection efficiency of cyclones SRI-IX
and SRI-X.

SUMMARY AND CONCLUSIONS

     Three systems have been developed and evaluated for the
purpose of sampling inhalable particles without reentrainment:
(1) a horizontal elutriator for sampling fugitive and ambient
aerosols, (2) a cyclone precollector to be used in-stack with
cascade impactors, and (3) a series-cyclone train for in-stack
use.  Each of the systems was calibrated under typical sampling
conditions and found to perform within the range specified for
samplers of inhalable particles.  A fourth method, a high volume
impactor, was tested and rejected because of poor performance
due to particle bounce.

     Second generation versions of the systems have been con-
structed for use in the field to determine emission factors for
inhalable particles from stationary sources.

ACKNOWLEDGEMENT

     This research was supported by the U.S. Environmental Pro-
tection Agency under contract 68-02-3113.


REFERENCES

 1.  Corn, M., and F. Stein.  Re-entrainment of Particles from
     a Plane Surface.  Am. Ind. Hyg. Assoc. J.  26:325-336, 1965.

 2.  Rao, A.K., and K.T.  Whitby.  Non-ideal Collection Character-
     istics of Single Stage Cascade Impactors.  Am. Ind. Hyg.
     Assoc.  J. 38:174-179, 1977.

 3.  Gushing, K.M., J.D.  McCain, and W.B. Smith.  Experimental
     Determination of Sizing Parameters and Wall Losses of Five
     Source-Test Cascade Impactors.  Environ. Sci. Technol.,
     13:726-731, 1979.

 4.  Fuchs, N.A.  The Mechanics of Aerosols.  Pergamon Press,
     New York, 1964.

 5.  Stein,  F., W.A. Esmen, and M. Corn.  The Shape of Atmospheric
     Particles in Pittsburgh Air.  Atmos. Environ. 3:443-453,
     1969.
                               346

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 6.  Rimberg, D., and J.W. Thomas.  Comparison of Particle Size
     of Latex Aerosols by Optical and Gravity Settling Methods.
     J. Colloid Interface Sci. 32:101-105, 1970.

 7.  Corn, M., F. Stein, Y. Harnmad, S. Manekshaw, W. Bell, S.J.
     Penkola, and R. Freedman.  Physical and Chemical Character-
     istics of "Respirable" Coal Mine Dust.  Ann. N.Y. Acad.
     Sci. 200:17-30, 1972.

 8.  Mercer, T.T.  Aerosol Technology in Hazard Evaluation.
     Academic Press, New York, 1973.  pp. 192-200.

 9.  Ranz, W.D., and J.B. Wang.  Impaction of Dust and Smoke
     Particles.  Ind. Eng. Chem.  44 (6):1371-1380, 1952.

10.  Marple, V.A.  A Fundamental Study of Inertial Impactors.
     Ph.D. Thesis, University of Minnesota, Mechanical Engineer-
     ing Department, Minneapolis. Particle Technology Laboratory
     Publication 144, 1970.  243 pp.

11.  Willeke, K.  Performance of the Slotted Impactor.  Am. Ind.
     Hyg. Assoc. J. 36:683-691, 1975.

12.  Rusanov, A.A.  Determination of the Basic Properties of
     Dust and Gases.  In:  Ochistka Dymovykh Gasov v Promyshlennoy
     Energetike [Cleaning Stack Gases in Industrial Power Engineer-
     ing] , A.A. Rusanov, I.I. Urbakh,  and A.P. Anastasiadi, eds.
     "Energiya," Moscow, 1969.

13.  Hochstrasser,  J.M.   The Investigation and Development of
     Cyclone Dust Collector Theories for Application to Miniature
     Cyclone Presamplers.  Ph.D.  Thesis,  University of Cincinnati,
     Cincinnati,  1976.

14.  Lippmann,  M.,  and T.L. Chan.   Cyclone Sampler Performance.
     Staub Reinhalt. Luft 39:7-12, 1979.

15.  Smith,  W.B.,  R.R.  Wilson,  and D.B.  Harris.   A Five-Stage
     Cyclone System for  In-Situ Sampling.   Environ. Sci.  Technol.
     13(11):1387-1392,  1979.

16.  John, W.G.,  P.  Reischl,  and J.J.  Wesolowski.  Size-Selective
     Monitoring Techniques for Particulate Matter in California
     Air.  AIHL/SP-12.   Final Report,  California Air Resources
     Board Contract No.  A5-00487,  1978.

17.  Chan, T.L.,  and M.  Lippmann.   Particle Collection Efficien-
     cies of Air Sampling Cyclones:  An Empirical Theory.   Environ.
     Sci. Technol.  11:377-382,  1977.
                               347

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                             PAPER 19
           DEPOSITION OF INHALED PARTICLES AND POSSIBLE
                         SAMPLING METHODS
                          VITTORIO PRODI
                         GIUSEPPE TARRONI
                          CARLO MELANDRI
                  LABORATORIO DI FISICA SANITARIA
                  DIPARTIMENTO  RADIAZIONI,  CNEN
ABSTRACT
     Inhalation is one of the most important routes of internal
contamination.  The efficiency of incorporation depends on aerosol
properties and on fluid dynamic properties of the airways.  In
this paper total and regional deposition in humans will be briefly
reviewed with the aim of understanding the basic mechanisms re-
sponsible for particle deposition and assessing the sensitivity
of deposition to the main aerosol, physiological, and possibly
pathological factors.  The available data on sampling efficiency
of the airways will be also reported in order to reach a detailed
picture of the overall transfer efficiencies.

     Two approaches to aerosol characterization for inhalation
toxicology will then be presented.  One is based on a direct
size distribution measurement with a recently proposed aerosol
spectrometer and the other is based on the simulation of the
regional deposition.  The first can be referred to the cut-off
sizes that are being introduced by EPA, while the second, if
a particular breathing pattern and individual deposition are
assumed, can yield directly the amount deposited in each region.

INTRODUCTION

     The atmospheric environment may contain airborne contami-
nants that pose serious risks of incorporation and then of toxic
action.  Particulate contamination is of great concern and is
of challenging difficulty to a quantitative assessment of in-
halation risks.

     Incorporation of particulate matter is a step process that
comprises inhalation of the aerosol, deposition of the  inhaled
aerosol, and clearance or translocation of the deposited aerosol,
and the final result is the retention of the contamination with
the resulting toxic action.


                               348

-------
     Each one of these steps has measured or measurable effi-
ciencies that depend on aerosol properties, on airways configura-
tion, and on respiration patterns.  Very detailed reviews have
been published by the ICRP Task Group1 on Lung Dynamics and by
Lippmann.2  Therefore here only the most recent results will
be reported, with emphasis on the parameters relevant to the
risk of incorporation.

Definitions

Inhalability:  is the probability for an airborne particle to
               enter the airways.3

Deposition:    is the probability for an inhaled particle to
               touch a surface of the respiratory tract and to
               adhere to it.3

Total deposition:  is such a probability referred to the entire
               respiratory tract.

               If a more detailed picture of the contamination
               is needed, the respiratory tract is divided into
               regions, characterized by predominant deposition
               and, for slowly soluble particles, clearance me-
               chanisms.  There is a generally accepted defini-
               tion of the regions:1'

Extrathoracic airways, in which the deposition is mainly due
               to inertia and particles are cleared within min-
               utes either by mechanical transport of particles
               or secretions.

Tracheobronchial airways, in which particles are deposited by
               inertia and settling and from which particles
               are removed within hours by mechanical transport
               of secretions.

Alveolar air spaces, characterized by small particle-to-wall
               distances, in which particles are deposited mainly
               by gravitational settling and brownian diffusion.
               The removal takes months or even years, mainly
               by phagocytosis, and subsequent cell transport
               to the mucociliary escalator or to the lymphatic
               system, or by dissolution.

Regional deposition is the probability for an inhaled particle
               to reach a surface of the given region and adhere
               to it.  Total deposition is the sum of regional
               depositions.
                               349

-------
Retention:     total retention is the probability for a deposited
               particle to be retained in the body, while regional
               retention is such a probability referred to a
               given region of the respiratory tract.

Deposition mechanisms:  particles are transported across stream-
               lines by a number of mechanisms: if they touch
               a surface, they deposit there.  The main mechanisms
               are gravitational settling, brownian diffusion,
               inertial impaction, and electrostatic attraction
               due to image forces.  Experimental data are avail-
               able for spherical or compact particles and here
               interception will not be considered.  All of these
               mechanisms are strongly size dependent.  Where
               aerodynamic effects prevail (settling and impac-
               tion) , the

aerodynamic diameter, of a particle, defined as the diameter
               of a 1 g cm   density sphere having the same settl-
               ing velocity as the particle, is a satisfactory
               and unique parameter accounting for deposition
               and aerodynamic techniques should be preferred
               for characterization.  Where diffusion prevails,
               since the diffusion coefficient is independent
               of density, the aerodynamic diameter is not repre-
               sentative and a

diffusive diameter should be introduced. **  This could be defined
               as the diameter of the sphere that has the same
               diffusive properties as the unknown particle.
               It is therefore important that characterization
               of an aerosol in this range should be based on
               diffusion or on techniques that can be uniquely
               related to diffusion.  In the case of very large
               densities the range of overlap of diffusion and
               aerodynamic effects varies and one can still have
               aerodynamic deposition with appreciable diffu-
               sive deposition.

AIR FLOW IN THE RESPIRATORY TRACT

     Deposition depends strongly on the flow which is effective
in airways, because it can affect the time-dependent mechanisms
through the mean residence time, MRT, (time dependent mechanisms
are settling and diffusion; electrostatic deposition is also
time-dependent,1"3 at least in the range 0.3 to 0.6 ym) and the
"prompt" mechanisms (impaction) through the volumetric flow
rate,3 VFR.  A detailed description of the aerodynamic properties
of the respiratory tract has been given by Lippmann2 and here
will just be briefly reported.
                               350

-------
     Respiratory frequency and tidal volume rule the MRT and
the VFR.  Mixing between tidal and residual air has a very im-
portant role in transferring inhaled particles into the residual
volume and thereby strongly increasing their residence time.
Mixing can take place in the conducting airways due to turbulence
and to vortices that even in laminar flow are established in
the bifurcations5 and propagate in the following branches.  The
mixing mechanism which is important in the whole respiratory
tract is due to the non-uniformity, both geometric and dynamic,
of the airways.  Their diameter in each generation is consider-
ably scattered; branching angles, also, are asymmetric; this
produces a non-uniform flow in the following bifurcations which
is not reversed in the exhalation.

     The overall effect is a considerable mixing.6  This has
been studied theoretically and an effective coefficient can be
introduced that accounts for the observed effect.7'8'9

     This non-uniformity can be enhanced by the relatively rigid
structures (blood vessels and bronchi) of the airways: during
expansion and contraction geometric similarity is not preserved.
The mixing effect is enhanced at lower values of the functional
residual capacity and this can account for the increased deposi-
tion with decreasing expiratory reserve volume,9 ERV.

     Accurate morphometric data are not available for populations;
it is not possible therefore to correlate the scatter of deposi-
tion values to any distribution of morphometric parameters, but
there is little doubt that this scatter should be due to anatomi-
cal as well as physiological or pathological differences.2

TOTAL DEPOSITION

     Total deposition has received greater attention than regional
deposition, since it can be studied in vivo with relatively simple
approaches.  Two techniques will be considered here:  one10'11'12
is based on the measurement of inhalation and exhalation flow
rates and particle concentration just at the entrance of the
airways.  The numbers of inhaled and exhaled particles and the
volumes are then computed by multiplication and integration.

     The other13 is based on the measurement of the particle
concentration averaged over several cycles with the volunteer
(exhalation)  and without the volunteer (inhalation) and on a
separate measurement of respiratory volumes.

     The two techniques have been recently compared and gave
coincident results.13

     Heyder and coworkers3'x ** have thoroughly investigated total
deposition, DE, as a function of route of inhalation, particle
size, and respiratory parameters.
                               351

-------
Size

     The  behavior of DE as  a  function of size  is  shown in Fig-
ure 1  (from Heyder et al.3) for  mouth breathing.   The general
trend  shows a minimum around  0.5 ym and increases both for de-
creasing  and for increasing size.   Below 0.5 ym  the increase
is due to increasing diffusion  coefficient.  Unfortunately in
the ultrafine range experimental data is scarce.15   Above 0.5 ym
deposition is due to gravitation and impaction.

MRT

     Figure 1 shows also  the  effect of MRT on  total deposition:3
DE increases with increasing  MRT because both  diffusion and set-
tling  are time dependent.   Impaction becomes important at higher
sizes  and this is shown by  the  smaller effect  of  MRT at high
VFR.
                   1.0
                 o
                   0.8
                 -.0.6
                 O
                 O 0.4-
                 LU
                 Q
                   0.2
                      MEAN RESIDENCE TIME, 1-8 s
                      VOLUMETRIC FLOW RATE. 250 cm3/s
                      PARTICLE DENSITY, 0.91 g/cm3
                           2468
                           PARTICLE DIAMETER, jum
10
        Figure 1. Effect of particle size and mean residence time on total deposition
               (from Heyder et a1.3).
                                 352

-------
VFR

     Total deposition  is  independent  of VFR up to  1  ~  1.5 ym
since  impaction is not  effective for  the range of  VFR  encountered.
At larger  sizes VFR begins playing a  more and more important
role,  as  shown in Figure  2 (from Heyder et al.3).   The importance
of impaction is depicted  in Figure 3,  where MRT and  VFR are varied
while  keeping the tidal volume  (TV) constant.  There is a definite
cross-over of the curves,  which is even more dramatic  for nose
breathing, as shown in  Figure 4 (also from Heyder  et al.3), where
it takes  place around  1 ym, showing the contribution of impac-
tion to nose deposition.
                   1.0
                   0.8-
                 o
                 1 0.6
                 •2.
                 g
                 H 0.4
                 CO
                 O
                 Q.
                 UU
                 a
                   0.2-
                       MEAN RESIDENCE TIME, 1 s
                       VOLUMETRIC FLOW RATE, 250-1000 cm3/s
                       PARTICLE DENSITY, 0.91 g/crn3	
                                                1000
                                                "750

                                                500
                                                250
                           2468
                           PARTICLE DIAMETER, jum
10
       Figure 2. Effect of particle size and volumetric flow rates on total deposition
              (from Heyder et al.3).
                                 353

-------
           1.0
               MEAN RESIDENCE TIME, 1-8 s           ]
               VOLUMETRIC FLOW RATE. 125-1000 cm3/s
               PARTICLE DENSITY, 0.91 9/cm3	
           0.8-
          o
           0.6
         O
         CL
           0.2
                                           _ 1  1000
                                              2   500
                                              4   250
                                              8   125
                      2468
                       PARTICLE DIAMETER, //m
10
Figure 3. Effect of particle size on total deposition for mouth breathing
         at 1000 c/r>3 tidal volume  (from Heyder et al.3).
            1.0
               'MEAN RESIDENCE TIME, V8 s
               VOLUMETRIC FLOW RATE, 125-1000 cm3/s
               PARTICLE DENSITY, 0.91 g/cm3	
            0.8-

          o
          *:
          u
          CD
          £ 0.6
          55 0.4
          O
          a.
          LU
          a
            0.2
                           1 1000
                           2  500
                           4  250
                           8  125
                       2468
                        PARTICLE DIAMETER, ptm
                                                    10
Figure 4. Effect of particle size on total deposition for nose breathing at
         1000 cm3 tidal volume (from Heyder et al.3).
                              354

-------
Biological  Variability

     It  is  now generally accepted2  that even under strictly con-
trolled  breathing conditions and  residual volumes there  is  a
definite intersubject variability of  total deposition.   An  ex-
ample of this  is given16 in Figure  5,  where the DE is plotted
as a function  of particle size between 0.3 and 1.5 ym unit  density
spheres  for  six volunteers, breathing  at 1000 cm3 TV and 15
respiration/min, each at his own  expiratory reserve volume,
ERV.  This  is  interesting since in  this range total deposition
is also  alveolar deposition.

     The scatter of data reaches  a  factor of 2 and cannot be
explained on the basis of respiratory  parameters.

     For  each  volunteer instead,  with  0.6 pro aerosols, a marked
dependence  on  ERV is found.  The  relative DE can be expressed
as a -1/3 power of the ERV relative to normal, probably  due to a
stronger  mixing with smaller volumes;9  a 10% variation of DE
corresponds  to a 30% variation of ERV  around the normal  value.16
             40
             30
           S20
           Q.
           111
           Q
       EXPIRATORY RESERVE
SUBJECT VOLUME, cm3
   15    1080
   24    1820
   6     1210

         1730

         1400
         2190
              0      0.5      1.0      1.5      2.0

                   SPHERE DIAMETER, urn, density 1 g/cm3
       Figure 5.  Total deposition for a group of 6 volunteers, at 1000 cm3 tidal
              volume and 15 respirations/min (from Tarroni et al. 16),
                               355

-------
Electric Charges

     Electric charges  carried by aerosol particles  have a definite
effect on deposition,  leading to an increased  efficiency.  This
has been found  in  deposition measurements of aerosols  produced
by atomization; when  the aerosol was not neutralized,  deposition
was higher and  poorly  reproducible.

     Quantitative  measurements16'17 have been  performed only
with monodisperse  particles charged with positive elementary
charges in a narrow number distribution and in controlled breath-
ing conditions.  The  electrostatic deposition,  shown  in Figure 6,
increases monotonically with increasing charge number  for 0.3
and 0.6 ym unit density spheres and is due to  image forces17
and therefore connected with the charge individually  carried.

     This has been confirmed theoretically18 in the concentra-
tion range considered.

     Quantitative  information on charge distribution of actual
aerosols is lacking;  for aerosols freshly generated by disruption
(grinding and atomization) the absolute charge can  be  very high
and its contribution  to total and regional deposition  should
be evaluated.
  16


  14


u? 12
Q

2 10
O

CO
O
QJ  6
Q
                    .SUBJECT 9
                    •SUBJECT 15
                                   0.6 j
                  0.3
                  10   20   30    40   50   60

                         ELECTRON CHARGES, n
                                   70   80
        Figure 6.  Contribution to total deposition from electric charges carried by
               0.3 and 0.6 yjn particles (from Tarroni et at. 16).
                                356

-------
REGIONAL DEPOSITION

Nose Deposition

     Nose deposition must be treated  separately since the  breath-
ing route can  be to some extent a matter  of choice for the sub-
ject, and has  peculiar clearance pathways;  this is important
both for total and regional deposition.

     Nose deposition data19'20'12'21'22  have been recently sum-
marized by  Lippmann2 and are shown  in Figure 7.

     The deposition is a linear function of the logarithm  of
the inertia parameter D2F when F is  the  VFR and is practically
quantitative for 9 ym particles at a  flow rate of 30 liters per
minute.

     The results are in fairly good  agreement with the ICRP Task
Group deposition curve, based on Pattle's23 data.

     Heyder and  Rudolf 21* have also successively studied  in detail
the deposition in the nose during exhalation, which is fairly
close to deposition during inhalation,  although this efficiency
applies only to  the transmitted fraction.
                     AERODYNAMIC DIAMETER AT 30g/min, M™

                            1     2    4  6 8 10   20
                   *  100
                                   1»»   O
                            RutfoM ft Hndv t»M
                                                10,000
           Figure 7. Head deposition during inhalation via the nose vs the impaction
                  parameter D?F (from Lippmann?).  The solid line is the
                  curve based on Pattle's23 data.
                                357

-------
Mouth Breathing

Extrathoracic Deposition—
     Regional deposition in mouth breathing has been studied
by Lippman,2 Lippmann and Albert,25 Chan and Lippmann,26 and
by Stahlhofen et al.27 by external counting of labeled deposited
particles.

     Head deposition too can be linearly fitted with the Ig D2F
parameter.  Lippmann's2 data have been extrapolated to obtain
the size for quantitative head deposition, which is around 17 urn
for a 30 8- min-1 VFR.

     Stahlhofen et al.'s27 data show a slightly higher efficiency
pointing to 100 percent deposition around 11 ym at the same flow
rate.

     The inertial parameter is not fully representative of deposi-
tion since the geometry of the airways may be dependent on the
flow.

     This should be  considered in establishing effective thresh-
olds of sampling instruments and guidelines.  In Figure 8 the
average extrathoracic deposition of three subiects27 is reported
for two flow rates together with Lippmann's curve.2

     In Figure 9 the effective total and regional depositions
are shown as the average of three subjects,   for two breath-
ing patterns:  TV =  1500 cm3, 15 resp.min"1  (MTR = 2 sec, VFR
= 750 cm3 sec"1) and TV = 1000 cm3, 7.5 resp.min"1  (MRT = 4 sec,
VFR = 250 cm3 sec"1)-  For the extrathoracic deposition the
curves are derived from the same data points of Figure 8.

Tracheobronchial Deposition—
     Tracheobronchial deposition has been studied in vivo by
Lippmann, Albert, and Peterson,28 on a large number of volunteers,
ranging from healthy non-smoking to smoking, mild bronchitic
and severe bronchitic.  Lately it has been studied by Chan and
Lippmann26 both in hollow casts and in vivo and by Stahlhofen,
Gebhart and Heyder27 on three healthy subjects.  In addition,
detailed studies have been performed on hollow  casts of human
bronchial trees by Chan, Schreck, and Lippmann,29 that have
pointed out the flow pattern in the trachea, and preferential
deposition sites in  connection with air flow and turbulence.
In addition the effect of electric charges on hollow cast deposi-
tion has been examined30 and the dependence on  image forces has
been confirmed.

     The studies of  Chan and Lippmann26 have shown a remarkable
biological variability of deposition data even  in the  tracheo-
bronchial tree.
                               358

-------
                        1.0-
                       0.8-
                       0.6-
        Volumetric flow/rate, cm3/s  250
        Mean residence time, s        4
        Subject 1                  O
        Subject 3                  A
        Subject 4                  D
            --- Lippmann (mean)
        Flow rate  370 - 680 cm^/s
        mean residence time 2.1 s
750
  2
                          103
Figure 8.  Head deposition during inhalation via the mouth  vs. impaction parameter.  The
          solid lines and points are for three subjects at two volumetric flow rates (from
          Stahlhofen et al.27)r while the broken line  is Lippmann's2 fitted curve.
                 z
                 o
                 00
                 O
                 a.
                 HI
                 0
                       1.0
                       0.8
,0.6-
 0.4-
                       0.2 i
                                       Mean residence time, 4s
                                       Volume flow rate, 250
                                       Mean residence time, 2s
                                       Volume flow rate, 750 cm-Vs
                                                             TOTAL
                               EXTRATHORACIC
                                       TRACHEO-
                                       BRONCHIAL
                          0        2       4       6       8       10

                                AERODYNAMIC DIAMETER, Mm

         Figure 9. Average total and regional depositions for three subjects at two
                   different respiratory patterns and for mouth breathing (based
                   on data of Stahlhofen et al.27).
                                         359

-------
      Figure  10  shows the TB deposition expressed  as a fraction
of  the aerosol  entering  the trachea.  The  straight  lines  rep-
resent the average and  the scatter of the  values  found by Lipp-
mann,2 while  the data of Stahlhofen et al.27 are  shown by the
points.   These  show a smaller scatter of data and two distinct
behaviors at  two rates  as well  as values of deposition slightly
lower than Lippmann's average.

      The actual tracheobronchial  deposition is a  bell-shaped
curve that departs from zero around or slightly above 2 ym aero-
dynamic size  and reaches a maximum, according to  the flow con-
ditions, between 6 and  10 ym.

      In Figure  9 the average actual TB deposition for three sub-
jects27 is plotted as a function  of particle size for two respi-
ratory patterns.
                 Q
                 i
CO
g
                    0.8
                    0.6H
                    0.4 H
                    0.2-
         Volumetric flow rate, cm3/s
         Mean residence time, s
         Subject 1
         Subject 3
         Subject 4
             ___ Lippmann (mean)
         Flow rate 370 - 680 cm3/s
         Mean residence time 2.1 s
                                            250  750
                                             42
                                             O   •
                                             A   A
                      103
                     10*
105
                                          cm
                                            3/s
        Figure 10.  Deposition in the ciliated tracheobronchial region during mouth
                 breathing, in percent of the aerosol entering the trachea.  The
                 straight lines represent the average and the scatter of Lippmann's^
                 data while the points are  the values obtained by Stahlhofen et al.27
                 (from Stahlhofen et al.27).
                                  360

-------
     It has been  pointed out that deposition depends  strongly
on the health  conditions and increases for smokers  and again
for bronchitic patients.  Chan and Lippmann26 have  proposed a
parameter, called the bronchial deposition size,  BDS,  derived
by expressing  tracheobronchial deposition as a  function of the
Stokes number.  This  was found to be 1.20 cm for  healthy non-
smokers, 1.02  for smokers, 0.9 for patients under treatment for
obstructive lung  disease, and 0.6 for severely  disabled patients.

     This effect  may  be important when establishing sampling
guidelines and in evaluating health hazards of  airborne particles
since it points out population groups particularly  at  risk in
some circumstances.

Alveolar Deposition—
     The gas exchange region of the airways is  characterized
by a very large surface area and therefore by a small  average
particle-to-wall  distance and a large cumulative  cross-section.
Therefore deposition  in the aerodynamic size range  is  practically
due to gravitational  settling.

     The alveolar deposition therefore increases  with  increasing
MRT at constant VFR.   Because of the behavior of  extrathoracic
and tracheobronchial  deposition, alveolar deposition  also follows
a bell-shaped  curve:  the relative maximum is around 3  urn and
can be shifted to smaller sizes both for increasing MRT at con-
stant VFR and  for increasing VFR at constant MRT.   In  the first
case the alveolar deposition values increase since  the extra-
thoracic and tracheobronchial deposition do not vary  appreciably
and gravitational deposition is more effective.   Figure 11, from
Heyder et al.,3 shows this effect in detail.
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                       TOTAL DEPOSITION	 8
                                            4
                                            2
                                       ALVEOLAR
                                       DEPOSITION
     02468

        PARTICLE DIAMETER, idtn
                                               10
        Figure 11.  Effect of particle size and mean residence time on total and
                 alveolar deposition (from Heyder et al.3).
                                361

-------
     Instead, the  increase  in  VFR causes a higher deposition
by impaction in the  higher  regions and therefore transmits a
lower fraction of  large  particles to the alveolar region and
the effect of increased  VFR covers the effect of decreased MRT.

     The data of Stahlhofen et al.27 for alveolar deposition
are also summarized  in Figure  9 as the average of their three
subjects.  These are  in  good agreement with.Lippmann and Albert's25
and Chan and Lippmann"s   data for comparable respiration pat-
terns.  These data are plotted together for comparison in Figure
12 (from Chan and  Lippmann26).  The scatter of these are larger
probably because of  the  larger number of subjects.  Consequently
intersubject variability is more considerable and the respiration
is not as strictly controlled.  This, though, makes them more
representative of  the range of values that one can find in a
population.

INHALABILITY

     Very little is  known on the efficiency of intake of the
airways for aerosol  particles  as a function of particle size,
respiratory conditions,  wind speed, and orientation of the head.
The only extended  work has  been done by Ogden and Birkett.31
Experiments were run  on  a tailor's dummy in a wind tunnel and
with wind speeds of  0.75 and 2.75 m sec"1  and orientations from
0° to 180°.

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               DIFFUSIVE DIAMETER, jum   AERODYNAMIC DIAMETER, pm


          Figure 12.  Alveolar deposition data of Chan and Lippmann26 and of
                   Stahlhofen et al.27
                                362

-------
     With 2.75 m sec"1 wind speed, already at 5 ym diameter the
aerosol is strongly oversampled for nose and mouth breathing
at 84 cm3 sec"1 VFR, is sampled faithfully at 335 cm3 sec"1,
and undersampled for higher VFR.  At lower wind speed the portal
of entry is not as important and the deviation of the sampled
concentration from the true concentration is at most of the order
of 25% above 15 - 20 ym.

     Orientation between 0° and 90° is very important: with a
5 £ min"1 VFR at 90° and with a wind speed of 0.75 m sec"1, the
nose can sample 5 ym particles with an efficiency almost halved
with respect to 0°.  At a higher wind speed and at 45° the nose
can strongly oversample, while the mouth samples always with
a reduced efficiency.

     Ogden and Birkett conclude that if the exposure is averaged
for all wind directions, to simulate a worker uniformly exposed,
the differences largely disappear and for winds between 0.75
and 2.75 m sec"1 and minute volumes between 20 and 40 5, for nose
and mouth breathing, the efficiency ranges as functions of the
aerodynamic diameter are shown in Table 1.
     TABLE  1.   RANGE  OF  ENTRY  EFFICIENCIES  FOR A HEAD RANDOMLY
         ORIENTED TO A WIND BETWEEN 0.75 AND 2.75 m  sec"1
	BREATHING WITH MINUTE VOLUME 20 - 40 LITERS3	


Aerodynamic
  diameter, ym       0     5     10     15     20     25      30

Efficiency
  range, %          100  68-83  46-72  39-67  33-60  31-55  30-52


a From Ogden and Birkett31
SENSITIVITY CALCULATIONS

     Particle deposition in the airways depends, as shown, on
many parameters.  Most of the measurements refer to laboratory
conditions and their bearing on industrial or environmental hy-
giene is not straightforward.  It is therefore interesting to
study the sensitivity of total and regional deposition to aerosol
parameters, respiration pattern, inhalation portal, and individual
variability.
                               363

-------
Total Deposition

     The data used for the sensitivity calculation are:

1)   total deposition curves as a function o£ particle size,
     respiratory frequency, and tidal volume for mouth and nose
     breathing obtained by Heyder and coworkers 1 **'3' 27 in the
     range 0.3 to 9 ym;

2)   intersubject variability between 0.3 and 1.5 ym and electric
     charge deposition values at 0.3 and 0.6 ym  up to 70 ele-
     mentary charges obtained at our laboratory.1*'17

     When not otherwise specified the aerosol was assumed log
normally distributed with a geometric standard deviation Og = 2,
which can be considered reasonable in many working environments;
the reference breathing pattern is 1000 cm3 tidal volume and
15 respirations min"1  (abbreviated 1000/15).

     The sensitivity to particle size is presented in Table 2
for mouth and nose breathing, where the data is  given as a per-
centage variation of deposition with respect to  a 1 um, Og = 2
aerosol.  The effect of size is very strong, especially for mouth
breathing, and can reach a factor of 3.
  TABLE 2.  TOTAL DEPOSITION; EFFECT OF MEDIAN SIZE OF PARTICLES

                     A% Deposition,               A% Deposition,
D, ym                mouth breathing              nose breathing
0.6
1.0
1.5
2
3
4
6
8
10
-28
_
+42
+81
+146
+193
+ 250
+281
+ 299
-33
„_.
+ 31
+ 52
+ 76
+87
+97
+ 100
+ 103
                               364

-------
     In Table 3 the effect of an increase of ag from 2 to 3 is
shown, as a percentage variation of deposition with respect to
the value at a  = 2, for mouth and nose breathing.  The effect
is especially remarkable again for mouth breathing.  The depend-
ence on a  is linear, so any a  can be evaluated.

     In Table 4, an example of the effect of biological vari-
ability is given:  it is remarkable at small sizes since the
absolute value is low.  At higher sizes deposition approaches
100% for all the subjects; little room is therefore left for
individual variations.
       TABLE 3.  TOTAL DEPOSITION: EFFECT OF AN INCREASE OF ag
                            FROM 2 TO  3

D, vim
0.6
1
1.5
2
3
4
A% Deposition,
mouth breathing
+35
+40
+27
+15
-1
-8
A% Deposition,
nose breathing
+39
+9
-5
-9
-9
-8

                      TABLE 4.  TOTAL DEPOSITION:
                         POSSIBLE INTERSUBJECT
                              VARIABILITY

D, ym
0.6
1
1.5
2
3
4
A% Deposition
±34
±26
±20
±17
±12
±9
                               365

-------
     The effect of the respiration pattern is shown, as a percent
variation in deposition with respect to 1000/15, in Table 5 for
mouth breathing and Table 6 for nose breathing.

     It can be remarked that 500/15 can be taken as reference
for the respiration at rest, 1000/15 for moderate activity and
1000/30 for strong physical activity.  The highest deposition
is found in the case of moderate activity. .

     Nose breathing is compared to mouth breathing in Table 7;
the data are the percent variation of nose breathing with respect
to mouth breathing.

     Table 8 summarizes the sensitivity calculations for the
various parameters in the specified ranges.  For the effect of
electric charges, the increase is referred to the 28 elementary
charges on 0.3 pm particles and 70 charges on 0.6 jam.  As was
observed above, unipolar charging is rare, but, since deposition
is by image forces, a comparable increase in efficiency could
take place with aerosols freshly produced by mechanical action
and not neutralized.
      TABLE 5.   TOTAL DEPOSITION:  EFFECT OF BREATHING PATTERN
	(VIA MOUTH)	

                	A% Deposition3	

                   TV = 500 cm3,                 TV  =  1000  cm3,
D, ym           15 respirations/min            30 respirations/min
0.6
1
1.5
2
3
4
6
8
10
-10%
-15%
-17%
-18%
-18%
-17%
-14%
-11%
-9%
-44%
-33%
-22%
-15%
-7%
-4%
-1%
-0
+1%

  With  respect  to  TV  =  1000  cm3,  15  respirations/min,
                               366

-------
    TABLE  6.   TOTAL DEPOSITION:  EFFECT OF BREATHING PATTERN
                           (VIA NOSE)

D, lam
0.6
1.0
1.5
2
3
4
6
8
10
% Deposition9
TV = 500 cm3,
15 respirations/min
-30%
-30%
-26%
-21%
-15%
-10%
-5%
-3%
-2%

TV = 1000 cm3,
30 respirations/min
+2%
+5%
+5%
+4%
+2%
+2%
+1%
0
0

With respect to TV = 1000 cm3, 15 respirations/min


                 TABLE 7.   TOTAL DEPOSITION:
                  PERCENT VARIATION OF NOSE
                  BREATHING WITH RESPECT TO
                       MOUTH BREATHING

D, ym
0.6
1.0
1.5
2
3
4
6
8
10
A% Deposition
+100
+ 115
+99
+80
+ 53
+38
+ 21
+14
+ 9
                             367

-------
     Only two values for each parameter are given since they
generally act in a different way for sizes greater or smaller
than 1.5 urn.

     In the range below 1.5 ym the inhalation route is the most
sensitive variable, while the others have the same effect and
have to be known with comparable accuracy.  Above 2 ym the ruling
parameter is particle size.

Aveolar Deposition

     The data available at the time the calculation was performed
were essentially the experimental alveolar deposition curve sum-
marized by Lippmann2 for mouth breathing, and, for nose breath-
ing, the curve calculated by introducing the nose deposition.
In the range below 2 pin the curves were completed with Heyder
et al.'s data14 of total deposition, since from 0.3 to 2 pm total
and alveolar deposition coincide.
  TABLE 8.   TOTAL DEPOSITION:  SUMMARIZED SENSITIVITY TO RELEVANT
 	AEROSOL AND RESPIRATION PARAMETERS	

                            Particle size
                              range, urn           A% Deposition
Size of particlesa
Geometric standard
deviation3
Electric charge
of particles3
Breathing pattern3
Inhalation route,
nose vs mouth
Intersubject
variability
0.6-1.5
2-10
0.6-1.5
2-10
0.3
0.6
0.6-1.5
2-10
0.6-1.5
2-10
0.6-1.5
2-10
300
30
40
10
35
65
30
15
100
80-10
30
10

  Mouth breathing
                               368

-------
     In Table 9 the effect of size is shown, for mouth and nose
breathing respectively; the effect of changing ag from 2 to 3
is shown separately for the inhalation portal in Table 10 and
the percent decrease in alveolar deposition when inhaling through
the nose with respect to mouth breathing is shown in Table 11.

     As in the case of total deposition, the parameter sensitivity
is summarized in Table 12.  The alveolar region is an organ at
risk for "insoluble" particles  (or better, slowly transferable
materials); Table 12 therefore can be taken as an indication
of the uncertainties one faces as far as deposition is concerned
when the aerosol is completely unknown.  Alveolar deposition
is less sensitive to size, standard deviation, and inhalation
portal than total deposition.

     Unfortunately more data is needed, especially for charged
particles,  for a complete assessment; nevertheless it can be
stated that the uncertainties of the inhaling subject (respira-
tion pattern, route of entry, biological variability) are com-
parable to the uncertainties of the aerosol characterization.

     Some aspects of these will be dealt with in the following
section, but it should be stressed here that, for a realistic
evaluation of inhalation risks, more data is needed also on
oxygen demand, minute volume, frequency, individual variability
of deposition, and route of inhalation.
       TABLE 9.  ALVEOLAR DEPOSITION: EFFECT OF MEDIAN SIZE
                           OF PARTICLES
                     A% Deposition,               A% Deposition,
D, iam                mouth breathing              nose breathing
0.6
1
1.5
2
3
4
6
8
10
-25
-
+26
+40
+45
+32
0
-33
-54
-12
-
+11
+13
+3
-13
-43
-63
-76
                               369

-------
TABLE 10.  ALVEOLAR DEPOSITION: EFFECT OF AN INCREASE OF
                     qq FROM 2 to 3

D, ym
0.6
1
1.5
2
3
4
A% Deposition,
mouth breathing
+22
+13
-10
-25
-38
-35
A% Deposition,
nose breathing
+19
+2
-16
-27
-32
-22

                TABLE 11.   ALVEOLAR DEPO-
              SITION: PERCENT VARIATION  OF
               NOSE BREATHING WITH RESPECT
                   TO MOUTH BREATHING

D, vim
0.6
1
1.5
2
3
4
6
8
10
A% Deposition
-19
-31
-39
-44
-51
-54
-59
-62
-64
                          370

-------
POSSIBLE SAMPLING METHODS

     At our laboratory we have essentially  followed  two  approaches
to aerosol characterization for inhalation  risk assessment, be-
sides the consolidated techniques that are  generally in  use.

     One is based on a simplified size spectrometry  that can
be used in the field and the other  is based on the simulation
of the total and regional deposition in the human respiratory
tract.

The Inertial Spectrometer

     Size characterization in the field is  now performed by means
of cascade impactors.32  These are  simple instruments and  so
well known that any description is  redundant here.   They have
been improved in recent years and have greatly profited  from
theoretical studies.33?3"  Nevertheless the usual drawbacks have
only partially been overcome; particle bouncing and  reentrainment
are still problems.  Vapor supersaturation  across the last stages,
which may increase particle mass by condensation, has also to
be considered.35  Cascade centripeters36 and generally virtual
impactors have improved the performance as  far as stage  loading
is concerned, but the wall losses may become a problem.

     Sampling cyclones have been greatly improved3 7~'11 with the
aid of semiempirical theories.  Sharp cut-offs have  been obtained
together with good classification performance.  These are par-
ticularly useful in high concentration environments  since par-
ticle bouncing and reentrainment can be avoided.

     A new instrument has been recently described1*2  that works
as a continuous spectrometer, has no moving parts, and collects


  TABLE 12.   ALVEOLAR DEPOSITION:  SUMMARIZED SENSITIVITY TO SOME
	OF THE RELEVANT PARAMETERS	

                            Particle size
                            range,   ym             A% Deposition
Size of particles3
Geometr icastandard
deviation
Inhalation route,
nose vs mouth
0
0
0
.6-1.5
2-10
.6-1.5
2-10
.6-1.5
2-10
25
40
20
30
30
50

  Mouth breathing
                               371

-------
tne whole aerosol  on  just one filter.  It is essentially  composed
of a 2-mm deep  rectangular channel, with a 90° bend, which is
flushed with clean air.   A thin aerosol sheath is  injected up-
stream of the bend; v.'hile the streamlines follow the curvature,
the particles,  because of their inertia, tend to persist  in their
initial velocity at the  bend.  Therefore the particles  depart
from the original  streamlines by a distance which  is a  function
of their aerodynamic  diameter.  The external wall  downstream
of the bend  is  made of a membrane filter through which  air is
sucked.  The particles are separated according to  size  while
airborne; the small separation is strongly magnified by the aero-
dynamic projection to the filter surface.  The filter will then
collect the  whole  aerosol: the particles too small to be  diverted
will be collected  toward the end of the filter,  large particles
are precipitated at the  beginning, and the intermediate sizes
are continuously separated,  The deposit can then  be analyzed
to yield the aerodynamic activity diameter, mass diameter, and
elemental size  distribution.  It could also be turned  into a
real time aerosol  spectrometer since the ceiling has no other
function than flow containment and can house appropriate  detectors

     The total  flow rate in the present version  is 7  £pm and
the aerosol  sampling  rate can reach 1/10 of that5  while still
preserving good resolution.  A high resolution run with 0.5,
1.14, and 2.01  urn  latex  spheres sampled separately is  shown in
Figure ±3.
         Figure 13.  Deposition pattern of 0.5, 1.14, and 2.01 urn latex particles
                  sampled separately with the inertial spectrometer. The singlet
                  and mu/tip/et fines of 1.14 and 2.01 spheres are clearly visible.
                                372

-------
     An example  of  a  calibration curve is shown in Figure  14.

     This  spectrometer  could meet the proposed sampling criteria
of EPA1*3 by working at  a reduced flow rate.  The deposit could
then be cut into three  sections: sizes greater than 15 ym,  be-
tween 15 and  2.5 urn,  and below 2.5 ym and each section could
be analyzed for  the quantity needed for toxicological evaluation.
In fact membrane filters are of controlled composition and  are
an ideal means for  environmental chemical analysis.  The filter
can be easily stored; the procedure could be greatly simplified
since the  filter  could  be evaluated only in the case, for ex-
ample, when a total particulate sampling would exceed a predeter-
mined investigation level.

     For general  application to size distribution measurements,
the deposit can  be  scanned and a signal can be obtained that
is a function of  the  amount of material contained in each size.
Examples of these could be radiometric scanning in the case of
radioactive materials,  X-ray fluorescence scanning, or optical
scanning of the  diaphanized filter.   Otherwise the filter can
be cut, with  the  aid  of the calibration curve, in equal loga-
rithmic intervals and the amount of material contained in each
          E

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 9

 8



 6

 5

 4-

 3

 2

 1

 0
                   5   10  15  20   25   30  35   40   45  50

                           DEPOSITION DISTANCE, mm
               Figure 14.  Calibration curve of the inertial spectrometer.
                               373

-------
section  analyzed with standard microchemical techniques.   The
cumulative  or  differential distribution can be obtained  of the
mass or  activity and then the activity median or mass  median
aerodynamic diameter can be obtained.   For each size fraction
the inhalability and deposition  can be readily computed  even
with a desk-top programmable microcomputer, for the particular
conditions  of  the individual involved.

     Figure 15 shows the distribution  of sodium chloride par-
ticles labelled with uranine as  analyzed with fluorescence tech-
niques.

     If  necessary, the aerosol can be  humidified in order to
let the  hygroscopic particles grow by  water condensation.  The
pressure drop  across the bend is too low to cause any  appreciable
modification of the aerosol before deposition.
                 99.9
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                   20
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                          PARTICLE DIAMETER, urn


       Figure 15.  Cumulative mass vs. size of a uranine-tagged sodium chloride
                aerosol sampled with the inertial spectrometer and determined
                by fluorometry.
                                374

-------
 Deposition  Simulating  Sampler

     Another  approach  has  been  already  described1*  and has been
 recently  developed  into  a  field sampler,  taking  also into ac-
 count  the most  recent  data on total  and regional deposition.

     It  is  based  on the  simulation of the total  and regional
 deposition  of particles  in the  human respiratory tract.

     In  this  way  the size  characterization of  the  aerosol is
 not  needed; the approach is then simpler  than  size spectrometry
 but  it  is not as  flexible  in the sense  that a  particular  respira-
 tory pattern  has  to be assumed  as a  reference.

     Bubbles  of aerosols freely rising  through a water column
 experience  a  particle  deposition by  inertia, sedimentation, and
 diffusion.  The combination of  these mechanisms  produces  a deposi-
 tion behavior which is quite close to absolute alveolar deposi-
 tion in  the respiratory  tract.   Therefore if,  before the  bubbler,
 a  stage  is  added  with  a  deposition efficiency  of the tracheo-
 bronchial plus  extrathoracic airways, what is  captured in each
 stage  is  a  measure  of  the  effective  regional deposition.

     In  the present set-up the  first stage is  composed of a dif-
 fusion humidifier and  a  specially designed cyclone.   The  sum
 of the deposition in the two stages  gives the  total deposition.
 This approach has the  advantage of inducing condensation  growth
 of the particles  where appropriate.  The  present set-up "*** has
 been checked  only for  particles larger  than 0.5  pm,  that  is,
 only in the aerodynamic  range.   It has  been previously shown,1*
 though, that  in the diffusion range  particles  are  captured in
 the  bubbles by  a  diffusion mechanism; this might be a more cor-
 rect approach than  pushing aerodynamic  separation  to sizes where
 aerodynamic effects play no role  in  particle deposition.

     There are  several parameters adjustable in  order to  vary
 the  deposition  efficiency:  the  height of  the water  column, by
 which the residence time of  the bubble  in water  can be varied;
 the  number and  diameter  of the  bubbling nozzles, by which the
 bubble diameters can be  to some extent  adjusted  and the impaction
 efficiency during bubble formation can  be affected.

     For  the  evaluation  of the  deposit  there are two possibili-
 ties:  either the material in each stage  is recovered and mea-
 sured or parallel lines  can  be  assembled,  each containing one
 stage more than the  other  and terminating with a membrane filter.
 The difference  in the  filter content would then  be  attributed
 to the capture  of the  missing stage  or  stages.

     The drawback of this  approach is again that it  matches one
particular respiratory pattern  at a  time  and it  has  to be re-
adjusted  to match other  conditions;   this  is essentially equi-
valent to selecting  a  reference condition or threshold that
always causes some  rigidity  in  the system.


                              375

-------
     In Figure 16 the deposition  efficiencies obtained in the
sampler are  shown by the experimental points as  a  function of
the particle size.

     For  comparison the deposition efficiency in humans3  is shown
with the  solid lines, for 1500/15 and mouth breathing.

CONCLUSIONS

     The  deposition efficiency  in the human respiratory tract
depends strongly on respiration pattern, portal  of inhalation,
minute volume and individual  variability besides aerosol proper-
ties, like particle size, shape,  electric charge,  and solubility.

     Therefore,  fixing particular particle sizes as a threshold
has a meaning only if referred  to particular breathing situations
and for particular aerosols;  consequently the need arises for
safety factors that invariably  make the evaluation of the inhala-
tion hazard  less and less realistic.
  100-
   90-

S  "
2  70H
w  60
o
2i  50
Q
   40
   30
   20
   10 -I

    0
                                                TOTAL
                                             EXTRATHORACIC +
                                             TRACHEOBRONCHIAL
                        234567


                         AERODYNAMIC DIAMETER, jum
        Figure 16.  Deposition efficiency in the simulating sampler44 (dots), as
                 compared with the total alveolar deposition in humans for
                 mouth breathing, 1500/15,3 (solid line).
                                 376

-------
     The more rigorous approach would then be a direct evaluation
of particle size distribution and of other aerosol properties.
These could be introduced into the appropriate inhalability and
deposition functions; then the effective deposition  in the real-
istic situation could be computed.

     This approach may appear like requesting more resources
than the evaluation of just two or three fractions.  The  amount
of resources needed can be decreased if total dust is sampled
together with the aerosol for size distribution.  The aerosol
could then be characterized only if the total dust sample exceeds
a prefixed investigation level or whenever the circumstances
would suggest to do so.

REFERENCES

 1.   Morrow,  P.E.,  Chairman.   ICRP Task Group Report on Lung
     Dynamics:  Deposition and Retention Models for Internal
     Dosimetry of the Human Respiratory Tract.  Health Phys.
     12:173-208,  1966.

 2.   Lippmann,  M.  Regional Deposition of Particles in the Human
     Respiratory Tract.   In:   Handbook of Physiology, Section
     9:   Reaction to Environmental Agents.   D.H.K. Lee,  H.L.
     Falk, S.D.  Murphy,  and S.R.  Geiger, eds.  Bethesda,  MD,
     American Physiological Society,  1977.   pp.  213-232.

 3.   Heyder,  J.,  J.  Gebhart,  and W.  Stahlhofen.   Inhalation of
     Aerosols;  Particle Deposition and Retention.   Presented
     at American Chemical Society Annual Meeting,  Symposium on
     Aerosol Generation and Exposure Facilities,  April,  1979.

 4.   Melandri,  C.,  and V.  Prodi.   Simulation of the Regional
     Deposition of  Aerosols in the Respiratory Tract.  Am.  Ind.
     Hyg. Assoc.  J.  32:52-57,  1971.

 5.   Schroter,  R.C., and M.F.  Sudlow.   Flow Patterns in Models
     of the Human Airways.   Respir.  Physiol.  7:431-455,  1969.

 6.   Ultman,  J.S.,  and H.S.  Blatman.   Longitudinal Mixing in
     Pulmonary Airways.   Analysis of Inert Gas Dispersion in
     Symmetric Tube Network Models.   Respir.  Physiol. 30:349-
     367, 1977.

 7.   Taulbee,  D.B.,  and C.P.  Yu.   A Theory of Aerosol Deposition
     in the Human Respiratory Tract.   J. Appl. Physiol.  38:77-
     85, 1975.

 8.   Yu, C.P.,  and  D.B.  Taulbee.   A Theory for Predicting Respira-
     tory Tract Deposition of Inhaled Particles in Man.   In:
     Inhaled Particles IV,  W.H.  Walton, ed.  Pergamon Press,
     Oxford,  1977.   pp.  35-46.
                                377

-------
 9.  Taulbee, D.B., and C.P. Yu.  Theory of Particle Deposition
     in the Human Lung.  Presented at Annual Meeting, Gesell-
     schaft fiir Aerosolforschung, Bad Soden, Germany, 1976.

10.  Muir, D.C.F., and C.N. Davies.  The Deposition of 0.5 ym
     Diameter Aerosols in the Lungs of Man.  Ann. Occup. Hyg.
     10:161-174, 1967.

11.  Heyder,  J., J. Gebhart, G.  Heigwer, C. Roth, and W. Stahl-
     hofen.  Experimental Studies of the Total Deposition of
     Aerosol Particles in the Human Respiratory Tract.  J. Aero-
     sol Sci.  4:191-208, 1973.

12.  Giacomelli-Maltoni,  G., C.  Melandri, V. Prodi, and G. Tarroni.
     Deposition Efficiency of Monodisperse Particles in the Human
     Respiratory Tract.  Am. Ind. Hyg. Assoc. J. 33:603-610,
     1972.

13.  Heyder,  J., J. Gebhart, C.  Roth, W. Stahlhofen, G. Tarroni,
     T. De Zaiacomo, M. Formignani, D. Melandri, and V. Prodi.
     Intercomparison of Lung Deposition Data for Aerosol Par-
     ticles.   J. Aerosol Sci. 9:147-155, 1978.

14.  Heyder,  J., L. Armbruster,  J. Gebhart, E. Grein, and W.
     Stahlhofen.  Total Deposition of Aerosol Particles in the
     Human Respiratory Tract for Nose and Mouth Breathing. J.
     Aerosol Sci. 6:311-328, 1975.

15.  Swift, D.L., F. Shanty, and J.T. O'Neil.  Human Respiratory
     Deposition Pattern of Fume-Like Particles.  Presented at
     American Industrial Hygiene Association Conference, May,
     1977.

16.  Tarroni, G., C. Melandri, V. Prodi, T. De Zaiacomo, M. Formi-
     gnani, and P. Bassi.  An Indication on the Biological Vari-
     ability of Aerosol Total Deposition in Humans.  Presented
     at American Industrial Hygiene Association Conference, May,
     1979.

17.  Melandri, C., V. Prodi, G.  Tarroni, M. Formignani, T. De
     Zaiacomo, F.G. Bompane, and G. Maestri.  On the Deposition
     of Unipolarly Charged Particles in the Human Respiratory
     Tract.  In:  Inhaled Particles IV, W.H. Walton, ed.  Per-
     gamon Press, Oxford, 1977.   pp. 193-203.

18.  Yu, C.P., and K. Chandra.  Precipitation of Submicron Charged
     Particles in Human Lung Airways.  Bull. Math. Biol.  39:471,
     1977.

19.  Hounam, R.F., A. Black, and M. Walsh.  Deposition of Aerosol
     Particles in the Nasopharyngeal Region of the Human  Respira-
     tory Tract.  Nature 221:1254-1255, 1969.
                               378

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20.  Lippmann, M. , and R.E. Albert.  Deposition and Clearance
     of Inhaled Particles in the Human Nose.  Ann. Otol. Rhinol.
     Laryngol. 79:519-528, 1970.

21.  Maertens, A., and W. Jacobi.   Die in vivo Bestimmung der
     Aerosolteilchen Deposition in Atemtrakt bei Mund-bzw-Nasen
     Atmung [The In-Vivo Determination of the Deposition of Aero-
     sol Particles in the Respiratory Tract by Mouth or Nose
     Breathing].  Presented at Annual Meeting, Gesellschaft fur
     Aerosolforschung, Bad Soden,  Germany, October, 1973.

22.  Rudolf, G., and J. Heyder.  Deposition of Aerosol Particles
     in the Human Nose.  Presented at Annual Meeting, Gesellschaft
     fur Aerosolforschung, Bad Soden, Germany, October, 1974.

23.  Pattle, R.E.  The Retention of Gases and Particles in the
     Human Nose.  In: Inhaled Particles and Vapors.  C.N. Davies,
     ed.  Pergamon Press, Oxford,  1961.  pp. 302-309.

24.  Heyder, J., and G. Rudolf.  Deposition of Aerosol Particles
     in the Human Nose.  In:   Inhaled Particles IV, W.H. Walton,
     ed.  Pergamon Press, Oxford,  1975.  pp. 107-125.

25.  Lippman,  M., and R.E. Albert.  The Effect of Particle Size
     on the Regional Deposition of Inhaled Aerosols in the Human
     Respiratory Tract.  J. Am. Ind. Hyg. Assoc. 30:257-275,
     1969.

26.  Chan, T.L., and M. Lippmann.   Experimental Measurements
     and Empirical Modelling of the Regional Deposition of In-
     haled Particles in Humans.  Submitted to Am. Ind. Hyg.
     Assoc. J.

27.  Stahlhofen, W., J. Gebhart, and J. Heyder.  Experimental
     Determination of the Regional Deposition of Aerosol Par-
     ticles in the Human Respiratory Tract.  Presented at American
     Industrial Hygiene Association Conference, May, 1979.

28.  Lippmann, M., R.E. Albert, and H.T. Peterson.  The Regional
     Deposition of Inhaled Aerosols in Man.  In:  Inhaled Par-
     ticles III, W.H. Walton, ed.   Unwin, London, 1971, pp.
     105-120.

29.  Chan, T.L., R.M. Schreck, and M. Lippmann. Effect of Tur-
     bulence on Particle Deposition in the Human Trachea and
     Bronchial Airways.  Presented at Annual Meeting, American
     Institute of Chemical Engineers, November, 1978.

30.  Chan, T.L., M. Lippmann, V.R. Cohen, and R.B. Schlesinger.
     Effect of Electrostatic Charges on Particle Deposition in
     a Hollow Cast of the Human Larynx-Tracheobronchial Tree.
     J. Aerosol Sci. 9:463-468, 1978.
                               379

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31.  Ogden, T.L., and J.L. Birkett.   The Human Head as a Dust
     Sampler.  In: Inhaled Particles IV. W.H. Walton, ed. Perga-
     mon Press, Oxford, 1977.  pp. 93-105.

32.  May, K.R.   The Cascade Impactor:   An Instrument for Sampling
     Coarse Aerosols.  J.  Sci.  Instrum. 22:187-195, 1945.

33.  Marple, V.A., and B.Y.H. Liu.  Characteristics of Laminar
     Jet Impactors.  Environ. Sci. Technol.  8:648-654, 1974.

34.  Marple, V.A., and K.  Willeke.  Inertial Impactors-Theory,
     Design and Use.   In:  Fine Particles, Aerosol Generation,
     Measurement, Sampling, and Analysis.   B.Y.H. Liu, ed.
     Academic Press,  New York,  1976.  pp. 411-446.

35.  Tarroni, G., C.  Melandri,  V. Prodi, M.  Formignani, and T.
     De Zaiacomo.  Taratura di una Centripeta in Cascata per
     Campionamenti di Aerosol in Diverse Condizioni Operative.
     [Calibration of a Cascade Centripeter for Sampling Aerosols
     under Diverse Operating Conditions.]  Presented at Annual
     Meeting, Italian Health Physics Society, Bologna, October,
     1977.

36.  Hounam, R.F., and R.J. Sherwood.   The Cascade Centripeter:
     a Device for Determining the Concentration and Size Distri-
     bution of Aerosols.  Am. Ind. Hyg. Assoc. J. 26:122-131,
     1965.

37.  Chan, T., and M. Lippmann.  Particle Collection Efficiencies
     of Air Sampling Cyclones:  An Empirical Theory.  Environ.
     Sci. Technol. 11:377-382, 1977.

38.  Lippmann, M., and T.L. Chan.  Cyclone Sampler Performance.
     In:  Proceedings:  Advances  in Particle Sampling and Measure-
     ment.  W.B.  Smith, compiler.  EPA-600/7-79-065, U.S. Environ-
     mental Protection Agency, Research Triangle Park, NC, 1979.
     pp. 30-51.

39.  Blachman, M.W., and M. Lippmann.   Performance Characteristics
     of the Multi-Cyclone Aerosol Sampler.  Am. Ind. Hyg.  Assoc.
     J. 35:311-316,  1974.

40.  Smith, W.B., K.M. Gushing, G.E. Lacey, and J.D. McCain.
     Particulate  Sizing Techniques for Control Device Evaluation.
     EPA-650/2-74-102a, U.S. Environmental Protection Agency,
     Research Triangle Park, NC,  1975.  p. 133.

41.  Smith, W.B., and R.R. Wilson.  Development and Laboratory
     Evaluation of a Five-Stage Cyclone System.  EPA-600/7-78-
     008, U.S. Environmental Protection Agency, Research Triangle
     Park, NC, 1978.  p.  59.
                               380

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42.  Prodi, V., C. Melandri, G. Tarroni, T. De Zaiacomo, M.
     Formignani, and D. Hochrainer.  An Inertial Spectrometer
     for Aerosol Particles.  J. Aerosol Sci. 10:411-420, 1979.

43.  Miller, F.J., D.E. Gardner, J.A. Graham, R.E. Lee, W.E.
     Wilson, and J.D. Bachmann.  Size Considerations for Estab-
     lishing a Standard for Inhaled Particles.   J. Air Pollut.
     Control Assoc. 29:610-615, 1979.

44.  Melandri, C., V. Prodi, G. Tarroni, M. Formignani, and T.
     De Zaiacomo.   Aerosol Sampling by Simulation of the Regional
     Deposition in the Human Airways.  Presented at Annual Meet-
     ing, Gesellschaft fur Aerosolforschung, Diisseldorf, October,
     1979.
                               381

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                             PAPER 20



         AEROSOL  SAMPLING  INLETS  AND  INHALABLE  PARTICLES
                        BENJAMIN  Y.H.  LIU
                          DAVID Y.H. PUI
                  PARTICLE TECHNOLOGY LABORATORY
                MECHANICAL  ENGINEERING DEPARTMENT
                      UNIVERSITY OF  MINNESOTA
ABSTRACT
     The problem of sampling aerosols from the ambient atmosphere
has been considered from a theoretical point of view.  Following
a review of the various samplers and inlets used in ambient sampl-
ing, the factors contributing to high sampling efficiency for
large particles are discussed.  It is pointed out that the major
mechanisms for particle loss in sampling inlets are impaction
on external surfaces, and impaction, turbulent deposition, and
sedimentation on internal surfaces.  Therefore, an efficient
inlet is one for which these losses are minimized.

     Based on these theoretical considerations, a new inlet for
sampling inhalable particles  (particles with aerodynamic diameter
of 15 um or less) has been designed, constructed, and tested.
The inlet incorporates an inlet configuration allowing for the
efficient entry of large particles into the inlet opening, fol-
lowed by an impactor to remove the coarse, non-inhalable par-
ticles.  The inlet has been found to have essentially wind speed
independent characteristics for wind speeds of up to 9 km/hr,
the maximum wind speed used in the tests.  The impactor used
has also been found to have sharp cut-off characteristics with
a sharpness of cut parameter, Og, of 1.18.  It is believed that
this particular inlet will meet the requirements of a high effi-
ciency inlet for sampling inhalable particles from the ambient
atmosphere.

INTRODUCTION

     Sampling of aerosols from the ambient atmosphere is an im-
portant and necessary first step in atmospheric aerosol measure-
ment.  To obtain accurate measurement results, a representative
aerosol sample must be drawn through an inlet into the particle
measuring or collecting device.  The sampling inlet is an im-
portant part of any aerosol measuring system and, as such, must


                               382

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be designed with care.  An ideal inlet should allow all particles
of interest to enter and arrive at the sensing or collecting
zone of the instrument while excluding rain, snow, insects, plant
matter, and other airborne debris.  The performance of the inlet
should also be unaffected by wind up to some maximum speed.

     Inhalable particulate matter (IPM) has been defined by the
Environmental Protection Agency1 as particles with aerodynamic
diameters of 15 ym or less.  New particulate air quality standards
based upon IPM are being developed by the Agency.  Unlike the
conventional high-volume sampler which measures the total sus-
pended particulates  (TSP) with an uncertain cut-off size for
large particles, samplers for IPM must have well-defined large
particle cut size characteristics.  The development of an inlet
of high efficiency for particles of up to 15 ym aerodynamic diam-
eter, therefore, is essential for the development of new IPM
standards.

     In this paper, we will first briefly review the various
approaches to ambient aerosol sampling, with particular emphasis
on the inlet designs.  A new inlet for the accurate sampling
of IPM will then be described, together with the criteria of
design and the performance data obtained on this new inlet.

AMBIENT AEROSOL SAMPLING AND INLET DESIGNS

     A principal requirement of ambient aerosol sampling is that
the instrument must be protected from rain and snow.  This can
be accomplished by means of simple weather-proof housings or
more elaborate inlet designs to achieve high inlet efficiency.
The term "inlet efficiency" is used here for the total trans-
mission efficiency of the inlet system, defined as the fraction
of particles transmitted by the inlet from the ambient atmosphere
to the sensing or collecting zone of the instrument.  For an
inlet of a specific design, the inlet efficiency is generally
a function of particle size, wind speed, and sampling flow rate.
High inlet efficiency can be achieved easily for small particles,
viz., those with diameters of a few micrometers or less.  How-
ever, for large particles, high inlet efficiency can be obtained
only with careful design.

High-Volume Sampler

     Figure 1 is a schematic diagram of the widely used high-
volume, or hi-vol, sampler.  The hi-vol sampler is the standard
reference method for TSP  (total suspended particulate) measure-
ment in the ambient atmosphere, in terms of which the national
ambient particulate air quality standards are defined.2  In the
standard hi-vol, a 20.3 cm x 25.4 cm  (8 in. x 10 in.) filter
is placed horizontally within the main sampler housing, which
is about 29 cm x 36 cm (11% in. x 14 in.) in cross-section.
The clearance area between the main housing and the roof at its
closest point is specified to be 580.5 ± 193.5 cm2  (90 ± 30 in.2).
Recent wind tunnel tests of the hi-vol by McFarland et al.3 showed


                               383

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that the D50 cut size  (aerodynamic  diameter  corresponding to
an inlet efficiency of  50%)  is  >30  ym at  a wind speed of 2 km/hr,
decreasing to about 30  ym  at  8  km/hr  and  17  ym at 24 km/hr.
In addition, the inlet  efficiency was found  to depend on wind
direction.  Table 1 shows  a  comparison of the inlet efficiency
of the hi-vol with several other ambient  aerosol samplers and
inlets.

Isokinetic Sampling

     In principle, isokinetic sampling can be used for atmospheric
sampling.  Although capable  of  high accuracy, isokinetic sampling
is seldom used because  the system to  achieve true isokinetic
conditions in the ambient  atmosphere  is necessarily complicated:
the inlet must be directed to face  the wind  and the suction speed
in the inlet must also  be  adjusted  to match  the wind speed.
The latter task is extremely  difficult to achieve under variable
wind conditions.
           Figure 1. Schematic diagram of the high-volume, or hi-volf sampler.
                               384

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      TABLE  1.  CHARACTERISTICS OF AMBIENT  AEROSOL  SAMPLERS
                            AND INLETS
 Sampler or inlet
     Reference
  D50  or  D
(Efficiency)
Wind speed,
  km/hr
Hi-vol


McFarland,
(1979) 3

et


al.


>30
30
17
ym
ym
ym
2
8
24
Rotating cowl

Rockwell inlet
Sehmel (1973)"

Willeke and McFeters
  (1975)6
 25  ym
SRI inverted inlet
Beckman dichotomous
sampler inlet

Sierra dichotomous
sampler inlet


Bird, et al. (1973)
McFarland, et al.
(1979) 3

Wedding and John
(1979)


5 5
5
5
12
12
12
15.
13
10.
11
22
15
10
ym (39%)
ym (30%)
ym (20%)
ym (35%)
ym (12%)
ym (35%)
5 ym
ym
5 ym
ym
ym
ym
ym
9.2
46
68
9.2
46
68
2
8
24
0
5
15
42

     In the "rotating cowl" sampler  (Figure 2) developed by
Sehmel,1* a wind vane was used to direct the inlet of a  56.6 Jl/min
(20 cfm) cascade impactor against the wind.  The suction speed
in the inlet was kept fixed at 1.9 km/hr.  Thus, the sampler
operated sub-isokinetically most of  the time, except near calm
air conditions.  The sampler was used to collect particles up
to 63 ym in diameter in a study of the resuspension of  soil par-
ticles by wind.

Inverted Inlet

     An inverted inlet may consist of a simple open-face filter
operating face down, as shown in Figure 3a, or an open-face
filter attached to a cylindrical tube, as shown in Figure 3b.
Figure 4 shows an inverted inlet designed and tested by Southern
Research Institute.5  The inlet efficiencies were found to be
39%, 30%, and 20%, respectively, for 5 ym diameter particles
at wind speeds of 9.2, 46, and 68 km/hr.  For 12 ym particles,
the efficiencies were 35%, 12%, and  35%, respectively,  at the
same wind speeds.
                               385

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              SYSTEM
              SUPPORT
              ARM
                                       HIGH VOLUME SAMPLER
                                     CASCADE IMPACTOR

                                 SPINDLE EXTENSION


WIND — •-

|
X
)
CYLINORICAI / / 1
WIND
DIRECTION
SENSITIVE
ROTATING
COWL
SAMPLE INLET / / \ •>
CYLINDRICAL «1S5^ WIND ORIENTATION
COWL


BODY «™""« TA|L (T|N
APPROXIMATE SCALE
25cm
Figure 2. The "rotating cowl" sampler described by Sehmel (1973)
                (o)
(b)
                      Figure 3.  The inverted inlet.
                                   386

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Circumferential  Side-Entrance  Inlet

     Figure  5  is an  omni-directional  inlet of  the  circumferential
side-entrance  type.   The  inlet,  designed  and built by  Rockwell
International  Corp.  at  the  suggestion of  the author  (Liu)  and
his  colleagues (K.T.  Whitby and  V.A.  Marple),  was  used in  EPA's
CHAMP  (Community Health Air Monitoring Program)  stations for
ambient  air  monitoring.   The inlet  incorporates  a  circumferential
impactor  to  remove coarse particles.   Tests by Willeke and McFeters6
showed that, at  the  sampling flow rate of 1133 fc/min  (40 cfm),
the  cut-point  of  the  circumferential  impactor  was  25 ym under
calm air  conditions.  However, no data on the  sampling efficiency
as a function  of  wind speed are  available.

     Figure  6  shows  another  inlet of  the circumferential,  side-
entrance  type.   The  inlet,  designed by McFarland et al.,   was
intended  for the  virtual  dichotomous  sampler.8  The same inlet
design is now  used in the commercial  dichotomous samplers  pro-
duced by  Beckman  Instruments,  Inc.  (Process Instrument Div.,
2500 Harbour Blvd.,  Fullerton, CA 92634) and Sierra Instruments,
Inc. (P.O.   Box  909,  Carmel Valley, CA 93924).  Tests  on the
Beckman  inlet  by  McFarland  et  al.3 showed that the D50 size of
the  inlet was  15.5 ym at  a  wind  speed  of 2 km/hr,  decreasing
to 13 and 10.5 ym, respectively, at wind speeds of 8 and 24 km/hr.
Similar  tests  by  Wedding  and John  (personal communication) on
the  Sierra inlet  resulted in D50 cut  sizes of  11 ym, 22 ym, 15 ym,
and  10 ym, respectively,  at wind speeds of 0,  5, 15, and 42 km/hr.

Wind Shield  and Baffles

     The  idea  of  using  a  wind  shield  or baffle to  minimize the
effect of wind on the inlet  efficiency was suggested by the
author (Liu) and  more fully explored  by Agarwal in an  internal
report at the  University  of Minnesota  Particle Technology  Labora-
tory.9

     Consider  the impaction of particles on a  cylindrical  object
of radius, R.  The impaction is  governed by the Stokes number,

          Stw= W  T/R                                           (1)

where W  is the wind  speed,  and T is the particle relaxation time
given by

          T  =  2 a2 PpC/9  y                                     (2)

where a is the particle radius,  Pp is  the particle density, C
is the slip correction, and y  is the gas viscosity.  For impac-
tion to occur, the Stokes number must  be larger than some  critical
value.   Thus,  by  choosing R to be sufficiently large,  impaction
can be prevented  for particles of a certain size up to a certain
maximum wind speed.
                               387

-------
INTERIOR SURFACES
TEFLON COATED
                                              BOLTS,  120° APART
                                                        RAINSHIELD
DECK PLATE
                                                 LOCK NUT
                                            SOCKET FOR M8 PLUG-IN
                                            (SAME AS NWL SHIP INLET)
      Figure 4.  The Southern Research Institute inverted inlet.5
                           HANDLE
                                                COVER
                                                    WATER DRAIN
                                                 AFTFR FILTER
                                          VACUUM PUMP
     Figure 5.  The Rockwell circumferential side-entrance inlet.
                                388

-------
     If particles  are  to be sampled into a tube of a radius
r, and the  tube  is placed at a right angle to the wind,  particle
impaction at  the tube  entrance will occur if r is small.   How-
ever, if the  tube  is placed within a cylindrical wind shield
or baffle of  a radius  R, as shown in Figure 7, and R is  made
sufficiently  large, particle impaction on the wind shield  can
be prevented  for particles of the same size at the same  wind
speed.  If  particle impaction does not occur on the wind shield,
the aerosol concentration inside the wind shield must be the
same as the concentration outside.  Unbiased sampling can  then
take place  from  the relatively calm air region within the  wind
shield.  However,  no systematic study of the wind shield idea
has been made, and the actual performance of the wind shield
remains unknown.

     Figure 8 shows the inlet of a virtual dichotomous sampler
described by  Dzubay et al.10 incorporating a wind shield.  In
this inlet, an auxiliary blower operating at a relatively  high
sampling flow rate of  200 &/min draws in air from around the
wind shield into the annular space, forming a downward-moving
jet.  Large particles  above 20 ym continue to travel down  because
of their inertia,  while smaller particles are drawn in through
the circumferential slit opening into the vertical sampling pipe,
where they  are sampled isokinetically at a rate of 14 £/min into
the dichotomous  sampler.  No performance data on this inlet were
given.
                    -H Mem
                     INLET
                     FLOW"
 V"
 •* V *-
 )CC
 )C
                                      NTERNAL INLET
                                  •-FLOW
                                        STILLING
                                       "CHAMBER
           INLET
          "FLOW
                   (b)
OUTLET
 FLOW
          Figure 6. The McFarland et al. circumferential side-entrance inlet.7
                               389

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THEORETICAL CONSIDERATIONS

     For an aerosol  inlet to be  efficient,  particle loss must
be small.  Particle  loss can occur  on the external surfaces of
an inlet or on internal surfaces.   Therefore,  an efficient inlet
is one for which both the external  and internal particle losses
are minimized.

     Consider, for instance, the circumferential, side-entrance
inlet shown schematically in Figure 9.  With horizontal wind,
particle impaction can occur on  the external surfaces of the
inlet because the streamlines  entering the inlet must make a
rather sharp turn at the entrance,  and the particle trajectories
can deviate from the streamlines of the flow.   This is depicted
in the upper half of the figure.  If the inlet is placed at a
distance which is not too far  from  the instrument housing, stream-
lines deflected by the instrument housing can also enter the
inlet at a rather sharp angle, causing additional impaction
losses to occur.  This is depicted  in the lower half of the
figure.  Therefore,  in designing aerosol inlets, both the ex-
ternal shape of the  inlet,  as  well  as the distance between the
inlet and the main instrument  housing, must be considered.
                                         —WINDSHIELD
                                           SAMPLING
                                            INLET
                 WIND-
                                           -WINDSHIELD
                                           -SAMPLING
                                            INLET
                        Figure 7. Wind shield or baffle.
                                390

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     Once  the particles  are brought  into an inlet by  the stream-
lines, additional loss can occur by  impaction, turbulent deposi-
tion, and  sedimentation.   Careful consideration of  all three
internal particle loss mechanisms must  be made in order to arrive
at a satisfactory design.   Loss of particles by Brownian dif-
fusion is  generally unimportant in aerosol inlets because of
the large  particle size  involved.
                                             DEFLECTOR
                                             RIM
                   o-* o
                    LU
                                                   INLET
                                                 WIND
                                                 SHIELD
                    ANNULAR
                    VIRTUAL
                    IMPACTOR
                                        200£/mirT
                                        TO BLOWER
                                 14 C/min
                           TO PARTICLE SEPARATOR
         Figure 8. The wind shield inlet for the virtual dichotomous sampler. 10
                                 391

-------
     A completely rigorous  theoretical approach to inlet design
does not exist at the present  time.   Much of the previous theo-
retical work on aerosol  inlets was  concerned with sampling under
calm air conditions,11"15 and  thus  was not applicable to ambient
sampling under wind.  Similarly,  the analysis of Davies16 and
Davies and Subari17 on the  sampling efficiency of a thin-walled
tube in a cross-wind, while interesting in showing the mechanics
of sampling, is not particularly  useful in inlet designs, since
the straight tube is known  to  perform poorly under moderate to
high wind conditions and is thus  not suitable as a general pur-
pose high efficiency inlet.  Thus,  instrument designers, when
faced with the problem of inlet design in the past, traditionally
took a rather empirical  approach,  and many of the resulting
inlets consequently have not performed too well.

     In the following discussions,  we will show that it is not
necessary to have a completely rigorous theoretical solution
to the problem before an efficient  inlet can be designed.  We
will show that, with a qualitative  understanding of the fluid
and particle mechanics involved,  a  satisfactory inlet can be
designed.
                  WIND
— STREAMLINE
— PARTICLE
  TRAJECTORY
           Figure 9. Streamlines and particle trajectories around an aerosol inlet.
                               392

-------
     Consider the three  inlet configurations  shown in Figure 10.
A simple vertical tube is used to  sample  the  ambient  aerosol
into the instrument.  With horizontal wind, particle  im-
paction near the upstream side of  the tube can  occur  because
of the bending of the streamlines  there.  In  Figure lOb, a cir-
cular flange is placed over  the  top of  the vertical tube to
deflect the streamlines  which would otherwise enter the tube
from below.  The flange  keeps the  streamlines straight prior
to their entry into the  tube, thus eliminating  particle loss
by external impaction.   Therefore/ the  design of  Figure lOb is
inherently a more efficient  design than that  of Figure lOa.
Similarly, in Figure lOc, the horizontal  entrance near the top
is enlarged compared to  that in  Figure  lOb.   This causes the
streamlines to bend more gradually while  entering the inlet,
resulting in reduced impaction loss on  the internal surfaces.
Thus, of the three inlet designs shown  in Figure  10,  the design
of Figure lOc should be  the  most efficient.

     The inlet configuration of  Figure  lOb, and,  by extension,
that of Figure lOc, are  similar  to the  case analyzed  theoreti-
cally by Zebel.18  Zebel showed  that, for an  inlet consisting
of a slit or hole in an  infinite wall,  the aspiration efficiency
can be approximated by the equation
Ei  ~
                   1.09St
                                                               (3)
                         w
                               WIND
               (a)
                      I

                      (b)
(0
                Figure 10.  Comparison of three aerosol inlets.
                               393

-------
where the aspiration efficiency  is  the  ratio  of  the  number of
particles carried by the flow through the  inlet  opening to the
number of particles in the original air  volume  in the ambient
atmosphere, and Stw is the Stokes number based  on wind velocity.
In Zebel's calculation, potential flow  was  assumed.   Figure 11
shows the streamlines near the entrance  to  the  slit  or hole for
the case where the wind speed, W, is equal  to the suction speed
in the slit or hole.

     Figure 12 shows the performance of  a  sampling inlet pre-
dicted by Zebel's equation for a circular  inlet  of 9.2 cm
(3-5/8 in.) diameter.  The result shows  that, for particles of
15 ym aerodynamic diameter, the  aspiration  efficiency is essen-
tially 100% at low wind speeds,  decreasing  to 90% at a wind speed
of 25 km/hr and 80% at 57 km/hr.  Thus,  Zebel's  results suggest
that it should be possible to design an  inlet to sample inhalable
particles efficiently.  The inlet performance can also be made
reasonably independent of wind speed up to  some  rather high wind
speeds.

A NEW IPM INLET

     On the basis of the above considerations,  we have designed
the inlet shown in Figure 13 for sampling  inhalable  particles.
The specific  inlet has been designed for the  virtual dichotomous
sampler, and  for a sampling flow rate of 1  m3/hr or  16.7 i/min.
         Figure 11. Streamlines over a slit or hole inlet in an infinite wall.
                               394

-------
   #80
   G60
   040 -
   c
   £
   in
   '20-
            INLET  DIAMETER-9.2cm (3
                            46       10

                              WIND SPEED, ktn/hr
                                                      2O
40     60
    Figure 12.   Efficiency of the ideal "hole in an infinite wall" inlet.
                                            CIRCULAR COVER
                                                     SPACER (3)
                                            SUPPORTING WIRE (3)


                                            IMPACTION NOZZLE
                                            IMPACTION CUP
                              \       /
                                  -•V-
Figure  13.   The University of Minnesota aerosol inlet for inhalable particles.
                                   395

-------
In addition to the several features described above, the inlet
contains a circular top to keep out rain and snow, and an inter-
nal impactor to remove coarse particles above 15 ym.  This inlet
has been evaluated in the wind tunnel at various wind speeds
up to 9 km/hr, the maximum wind speed obtainable in our present
wind tunnel.  The experiments performed are described below,
together with the data obtained.

DEFINITION OF TERMS

     For purposes of describing the characteristics of the inlet
shown in Figure 13, the following efficiencies are defined:

     Ej = aspiration efficiency = n^/m,,                        (4)

     E2 = impactor transmission efficiency = m2/m1             (5)

     E  = total transmission efficiency of the inlet system,
          or the inlet efficiency = m2/m0 = EjE2               (6)

where

     mj = mass of particles carried by a given volume of flow
          through the exit plane of the impactor nozzle

     m2 = mass of particles carried by the same volume of flow
through the exit plane of the inlet system, and

     mo = mass of particles in the same volume of air in the
          ambient atmosphere.

All particle masses referred to above are for particles of a
certain size.

     The aspiration efficiency, Eir defined above, is similar
to the aspiration coefficient defined by Davies11 or the suction
coefficient defined by Zebel18  (Equation 3).  The only difference
is that the aspiration efficiency is defined in terms of the
particle mass passing through the exit plane of the impactor
nozzle, whereas the aspiration or suction coefficient is usually
defined in terms of the particle mass brought in by the flow
through the inlet opening, in this case, the top of the funnel.
Thus, the aspiration efficiency takes into account the particle
loss in the entrance portion of the impactor nozzle, whereas
the aspiration or suction coefficient does not.  However, since
particle loss in the funnel portion of the inlet has been found
to be small for particles in the inhalable size range, the dif-
ference between aspiration efficiency defined here and the aspira-
tion or suction coefficient defined by Davies and Zebel is not
large and, for all practical purposes, can be ignored.
                               396

-------
     The impactor transmission efficiency, E2, defined by Equa-
tion 5, is usually referred to as "penetration" in  impactor
studies.  However, in the present case, the impactor  is used
to remove the non-inhalable particles and to transmit the in-
halable particles efficiently.  The term "impactor  transmission
efficiency", therefore, appears appropriate.  Finally, the total
transmission efficiency of the inlet system, E, or  the inlet
efficiency for short, is the same as the "inlet effectiveness"
defined by McFarland et al.3>7  However, the term "efficiency"
is believed to be appropriate, since in engineering usage, ef-
ficiency generally means, and is usually defined as,  the ratio
of the desired output to the input.  For example, the efficiency
of a power plant is defined as the ratio of the energy output
of the power plant to the energy input.  In the present case,
the inlet system may be considered as a particle transmission
device, the desired output being the aerosol transmitted or
delivered to the sampling or measuring instrument,  and the input,
the aerosol drawn in from the ambient atmosphere.   Therefore,
the term "inlet transmission efficiency", or the "inlet effi-
ciency" for short, is appropriate and should cause  no confusion.

EXPERIMENTAL STUDY AND RESULTS

     The preliminary tests of the inlet completed were of two
main types.  In one type of test, the inlet was evaluated with
an optical particle counter in the wind tunnel and  its perfor-
mance compared with several other inlet configurations.  The
purpose of these experiments was to compare the relative per-
formance of the several inlet configurations in order to see
if the chosen configuration indeed had the highest  aspiration
efficiency.  For these experiments, the absolute value of the
aspiration efficiency was not needed.  In the second type of
test, the absolute aspiration efficiency of the inlet was mea-
sured, as well as the absolute impactor transmission efficiency
and the absolute inlet efficiency.  The measurement was made
by sampling the particles through the inlet and through an iso-
kinetic probe, and comparing the collected particle mass by
fluorometric analysis.

     The experiments were performed in the low-speed wind tunnel
facility of the Particle Technology Laboratory.  The wind tunnel
has a 50 cm x 50 cm (20 in. x 20 in.) test section  and is capable
of a maximum wind speed of 9 km/hr.  The projected  area of the
inlet in the direction of flow is about 125 cm2.  Thus, about
5% of the test section area was blocked by the inlet under test.
A complete description of the wind tunnel facility  has been given
by Whitby et al.*'

     Figure 14 shows the test setup for measuring the relative
performance of the inlets by means of an optical particle counter
(OPC).  Monodisperse aerosols of oleic acid were generated by
the vibrating orifice monodisperse aerosol generator  (Berglund
                               397

-------
and Liu20)  and  introduced into the wind tunnel.   The particles
were then  sampled into an optical particle  counter  (Royco 245,
Royco Instruments,  Inc., 141 Jefferson Drive,  Menlo Park, CA
94025)  through  the  different test inlets.   By  comparing the
counts  registered by the OPC when different inlets  were used,
the relative  performance of the inlets could be  determined.
For these  experiments, the impactor was removed  from the inlet
shown in Figure 13,  and the entire flow of  16.7  £/min passing
through the inlet was sampled into the Royco 245 counter.  The
geometrical diameter of the particle was calculated from the
liquid  flow rate, the solution concentration,  and the vibrating
frequency  in  accordance with the method described by Berglund
and Liu.    The  geometrical diameter was then converted to aero-
dynamic diameter by multiplying by the factor  /Pp,  where pp =
0.894 g/cm3  is  the  density of oleic acid.

     The inlets  tested included the UM inlet of  Figure 13 with
the circular  top and impactor cup removed—referred to here as
the reference inlet—, a funnel inlet (the  UM  inlet without the
top, flange,  and impactor cup), and two tube inlets consisting
of straight 5.08 cm  (2 in.)  and 3.81 cm (1.5 in.) diameter tubes
which were  placed perpendicular to the horizontal wind in the
wind tunnel.  Under  steady state conditions, the counts registered
by the OPC  over  the  same time interval represent the relative
efficiency  of the inlets tested.

     The results of  the above experiments are  shown in Figures 15,
16, and 17.   In  these plots,  the aspiration efficiency of the
inlets relative  to  the reference inlet is shown  plotted against
wind speed  for  particle aerodynamic diameters  of 12.8, 14.2,
and 15.6 urn.  In all cases,  the reference inlet  was found to
           MONODISPERSE
           AEROSOL FROM
           VIBRATING
           ORIFICE
           GENERATOR
                      FILTER (2)
X
PLATE
H i
X
JL h
r*-i
^— HEPA 1 	 1
rAIR FLO
I NOZZLE
\1_


     TO BLOWER
                                      ROYCO 245
                                      OPTICAL
                                      PARTICLE
                                      COUNTER
V
  MANOMETER
            Figure 14. Test setup for measuring the relative efficiencies of
                    different inlet configurations.
                                398

-------
have the highest aspiration efficiency and to  show the least
dependence  on wind speed.  For  example, comparing  the reference
inlet with  the 3.81 cm diameter  tube inlet, the  aspiration ef-
ficiency of the latter for 12.8  urn diameter particles is 90%
of that of  the reference inlet  at a wind speed of  3 km/hr.  How-
ever, at a  wind speed of 9 km/hr, the aspiration efficiency of
the tube inlet drops to only  12% of that of the  reference inlet.
It was also found that the addition of the circular top to the
reference  inlet did not change  its aspiration  efficiency.  There-
fore, the data obtained above were, for all practical purposes,
the same as the aspiration efficiency of the various test inlets
relative to the complete UM inlet of Figure 13.

     The absolute performance of the complete  UM inlet of Fig-
ure 13 was  evaluated in the wind tunnel with fluorescein-tagged
DOP  (dioctyl phthalate) aerosol  and by comparison  with an iso-
kinetic probe.  The aerosol was  generated by dissolving DOP and
fluorescein in isopropyl alcohol and spraying  the  solution through
                     1.0
                     0.9
                     0.8
                    (A
                    <0.6

                    O


                    2 0.5
                    u 0.4
                     0.3
                    §
                    i-
             SAMPLING
             FLOWRATE' I6.7lpm
OREFERENCE
 INLET (UM
 INLET WITHOUT   \\
 TOP AND IMPACTOR) \
 (BY DEFINITION)
 D 9.2 cm. FUNNEL

 A 5.1 cm TUBE

 O 3.8 cm TUBE
                                      \
                            369
                              WIND SPEED, km/hr
           Figure 15. Relative performance of several inlet configurations for
                    12.8 yuri diameter particles.
                                 399

-------
the vibrating orifice  droplet  generator.  The geometrical diam-
eter of the aerosol  was  similarly calculated from the droplet
generator operating  conditions and converted to aerodynamic  diam-
eter by multiplying  by /pp,  where pp = 0.980 g/cm3 is the density
of DOP.  Since  the amount  of fluorescein used was small  (about
2% of the DOP mass in  most cases), the slight increase in droplet
density due to  fluorescein addition was ignored.

     In these tests  with fluorescein-tagged DOP aerosol, a Milli-
pore filter was mounted  directly at the exit of the UM inlet
to sample the particles  passing through the inlet.  Following
sampling, the fluorescein  was  extracted from the filter  by im-
mersing the filter in  20 to 80 ml of 0.01 N aqueous solution
of NaOH.  The solution and filter were then agitated  in  an ultra-
sonic bath for  2  to  3  minutes.  The fluorescein concentration
in the solution was  then measured with a fluorometer  (Model  110,
G.K. Turner Associates,  Palo Alto, CA).  The filter at the exit
of the isokinetic probe  was similarly analyzed.  To measure  the
material deposited on  the  inside surface of the isokinetic probe,
H
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INLET (UM
INLET WITHOUT
TOP AND IMPACTOR)
(BY DEFINITION)

D 9.2 cm FUNNEL
A 5.1 cm TUBE
0 3.8 cm TUBE

                           369
                             WIND SPEED, km/hr
             Figure 16.  Relative performance of several inlet configurations
                      for 14.2 nm diameter particles.
                                400

-------
a wet cotton  swab was used to wipe the  inside surface of the
probe clean.   The cotton swab was then  immersed in 20 ml of wash
solution and  similarly agitated in an ultrasonic bath for 2 to
3 minutes  to  extract the fluorescein from  the cotton swab.  Gene-
rally, very little material was found on the  inside surface of
the isokinetic probe.

     To measure the material collected  on  the inside surface
of the impaction cup, the outside surface  was first wiped clean
with a wet cotton swab and 20 ml of wash solution was added to
the cup and ultrasonically agitated.  The  solution was then
analyzed.  The same cotton swab was then used to wipe the re-
maining surfaces in the inlet to determine the wall losses in
the inlet.  The cotton swab was then similarly analyzed.
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INLET 
-------
     From these measurements, the various efficiencies were cal-
culated as follows:

     Impactor transmission efficiency = mf/(m. + m  + m,)      (7)
                                         
-------
        100
                    5            K>           20
                         AERODYNAMIC DIAMETER, fj.m
Figure 18.   Experimental transmission efficiency of the impactor used
            in the University of Minnesota inlet.
          120
          IOO
          , so
         y eo
         u
         u.
         §40

         K
         z

         3 20
           0.5
                    Dp.
                 O   8.5

                 D   II.O
                 £.   I3.4
                                                         10
                         WIND SPEED,  kffl/hr
    Figure 19.   Experimental aspiration efficiency of the University
                 of Minnesota inlet.
                                403

-------
error of the measured aspiration efficiency  (about ±10%), the
aspiration efficiency is essentially 100%  for  particles of 8.5
and 11.0 ym aerodynamic diameter.  However,  for particles of
13.4 ym aerodynamic diameter, there appears  to be some decrease
in aspiration  efficiency at the higher wind  speeds.  This de-
crease in aspiration efficiency is larger  than that predicted
by Zebel's theoretical equation.  This suggests that the flow
field at the inlet is more complicated than.that assumed by Zebel
in his analysis.

     In Figure 20, the overall transmission  efficiency of the
inlet is shown.   The change in inlet efficiency with wind speed
is very slight and, for all practical purposes, negligible.
Since the maximum wind speed used in these tests was 9 km/hr,
it would be useful to see what changes in  inlet efficiency would
be expected theoretically for higher wind  speeds.  This can be
done by combining the experimental impactor  transmission effi-
ciency curve of  Figure 18 with the theoretical aspiration effi-
ciency of Equation 3.  The result, shown  in  Figure 20, suggests
that the inlet should work quite well and  not  show significant
wind speed dependent characteristics for wind  speed of 24 km/hr.

     In Figure 20, the characteristics of  the  present inlet are
compared with  those of the inlet used in  the Beckman dichotomous
sampler  (McFarland et al. 3).  The present  inlet is seen to be
considerably sharper in its cut-off characteristics.
                  IOO
                  80
                  60
                  20
                       WIND SPEED, km/hr
                     A
                     O
                     a
 EXPERIMENTAL


 EXTRAPOLATED
 FROM THEORY

 BECKMAN INLET
{McFARLAND el ol.,
   1979)


 i  i i  i I	
                                          \
                                           V
                         5       IO
                          AERODYNAMIC DIAMETER.
                                                  50
       Figure 20.  Experimental inlet efficiency for the University of Minnesota inlet
                and its comparison with the Beckman dichotomous sampler inlet.
                                 404

-------
      The  wall loss  data for  the present inlet are shown in Table 2,
 The  maximum wall loss observed is 8.1% for particles of 11.0 ym
 aerodynamic diameter, and the average wall loss for all the tests
 combined  is 1.85%.

 DISCUSSIONS, CONCLUSIONS, AND FUTURE WORK

      When using the inlet described above on an actual aerosol
 sampling  instrument,  the distance between the inlet and the in-
 strument  is important and must be considered.  If the inlet is
 installed too close to the main instrument housing, the situation
 depicted  in Figure  9  could arise where the streamline deflected
 upward by the housing could  interfere with the operation of the
 inlet, thereby degrading its performance.  It is recommended
 that the  distance between the inlet and the top of the main in-
 strument  housing be kept equal to or larger than the height of
 the  instrument housing, as shown in Figure 21(a).  If it is not
 possible  or desirable to have this minimum distance of separation
 between the inlet and the instrument housing, a horizontal de-
 flection  plate can  be installed over the top of the instrument
 housing,  as shown in  Figure  21(b), to prevent the streamlines
 deflected upward by the instrument housing from interfering with
 the  inlet operation.   With these precautions, it is believed
 that the  performance  of the  inlet, as determined for an isolated
 inlet in  a wind tunnel, should be the same as the actual perfor-
 mance of  the inlet  when installed on the instrument.
                  TABLE  2.   WALL  LOSS IN UM INLET
Wind speed, km/hr
Da,
Wall loss, %
1 5
8.5
11
13.4
16
18.5
0.9
1.0
8.1
0
0.1
0.9
                               11

                               13.4
                        3.0

                        0.4
                               11

                               13.4
                        3.8

                        1.3
                               405

-------
     Based on  the work  performed so far, we believe the inlet
described above will  meet  the basic requirement of an inlet  for
sampling inhalable  particles  from the ambient atmosphere.  How-
ever, the D50  diameter  of  the present inlet is 13.3 pm, which
is somewhat smaller than the  15.0 ym diameter that was intended.
The D5o diameter can  be increased by increasing the impactor
nozzle diameter slightly,  from the present value of 1.28 cm  to
1.39 cm.  This slight increase in nozzle diameter should not
affect the inlet operation in other respects.

     Before the present inlet is adopted for routine sampling,
it is desirable that  additional tests be performed.  In addi-
tion to wind tunnel testing at higher wind speeds, the inlet
should also be tested for  its actual field performance charac-
teristics.  Some limited tests have shown that the inlet is
weather-proof, at least for rain, i.e.,  the circular top is  ef-
fective in keeping  out  rain.   We believe that insects, plant
matter and other airborne  debris would,  by virtue of their large
size, be effectively  trapped  by the impact ion cup.  By coating
the inside surface  of the  impaction cup  with a non-volatile
grease, particle bounce and re-entrainment could also be pre-
vented.  Unlike other impactors designed for size classification
of small aerosol particles, the present  impactor operates at
a relatively low jet  velocity of 8.4 km/hr, which should minimize
the problem of particle bounce and re-entrainment.  In addition,
if coarse particles should bounce when they come in contact with
the bottom of  the cup,  they would lose much of their momentum
                      -INLET
                                            -INLET
                       INSTRUMENT
                       HOUSING
                                              /-DEFLECTOR
                                      -2H-
                                             INSTRUMENT
                                             HOUSING
             Figure 21.  Two methods of installing an inlet on an
                      aerosol sampling instrument.
                                406

-------
and energy and be subsequently caught by the vertical surfaces
in the impaction cup.  Therefore, we do not believe that particle
bounce and re-entrainment would be a problem for an impactor
of this particular design.

     In addition to the above, we have also designed an inlet
which is similar to the inlet described above, except that a
cyclone is used for separating the inhalable and non-inhalable
particles.  This new inlet will be evaluated and reported some-
time in the future.

ACKNOWLEDGEMENTS

     This research is supported by a grant, No. R804600, from
the Environmental Protection Agency.  The Agency's support is
gratefully acknowledged.  We also wish to thank Sandra Iverson
of the University of Minnesota for her able assistance in carry-
ing out some of the experimental measurements reported here.
This report is Particle Technology Laboratory Publication No. 397.

REFERENCES

 1.  Miller, F.J., D.E. Gardner, J.A. Graham, R.E.  Lee, Jr.,
     W.E. Wilson, and J.D. Bachmann.  Size Considerations for
     Establishing a Standard for Inhalable Particles.   J. Air
     Pollut. Control Assoc. 29:610, 1979.

 2.  National Primary and Secondary Ambient Air Quality Standards.
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 3.  McFarland, A.R., C.A. Ortiz, and C.E. Rodes.   Characteris-
     tics of Aerosol Samplers Used in Ambient Air  Monitoring.
     Presented at the 86th National Meeting of the American Insti-
     tute of Chemical Engineers, 1979.

 4.  Sehmel, G.A.  An Evaluation of High-Volume Cascade Particle
     Impactor Systems.   Presented at the 2nd Joint Conference
     on Sensing of Environmental Pollutants, Instrument Society
     of America, 1973.

 5.  Bird, A.N., Jr., D.V. Brady, and J.D. McCain.   Evaluation
     of Sampling Systems for Use of the M8 Alarm Aboard Ships.
     Report SRI-EAS-73-064, Southern Research Institute,  Birming-
     ham, AL, 1973.

 6.  Willeke, K., and J.J. McFeters.  Calibration  of the CHAMP
     Fractionator.  Particle Technology Laboratory Publication
     No.  252, University of Minnesota,  1975.

 7.  McFarland, A.R., J.B. Wedding, and J.E. Cermak.   Wind Tunnel
     Evaluation of a Modified Andersen Impactor and an Ail-Weather
     Sampler Inlet.  Atmos. Environ. 11:535, 1977.
                               407

-------
 8.   Dzubay,  T.G.,  and R.K.  Stevens.   Ambient Air Analysis with
     Dichotomous Sampler and X-Ray Fluorescence Spectrometer.
     Environ. Sci.  Technol.  9:663, 1975.

 9.   Agarwal, J.K.   The Sampling of Aerosols.  Particle Technology
     Laboratory Report No.  208,  University of Minnesota, 1972.

10.   Dzubay,  T.G.,  R.K. Stevens, and C.M.  Peterson.   Application
     of the Dichotomous Sampler  to the Characterization of Ambient
     Aerosols.  In:  X-Ray Fluorescence Analysis of  Environmental
     Samples, T.G.  Dzubay,  ed.   Ann Arbor  Science Publishers,
     Ann Arbor, MI, 1977.  p. 95.

11.   Davies,  C.N.   The Entry of  Aerosols into Sampling Tubes
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12.   Kaslow,  D.E.,  and R.J.  Emrich.  Aspirating Flow Pattern
     and Particle Inertia Effects Near a Blunt Thick-Walled Tube
     Entrance.  Department of Physics, Lehigh University, Beth-
     lehem, PA.  Technical Report No. 23,  1973.

13.   Kaslow,  D.E.,  and R.J.  Emrich.  Particle Sampling Efficiencies
     for an Aspirating Blunt Thick-Walled Tube in Calm Air.
     Department of  Physics,  Lehigh University, Bethlehem, PA.
     Technical Report No. 25, 1974.

14.   Kim, Y.W.  An  Analytical Consideration of the Particle In-
     ertia Effect with an Application to Aerosol Sampling Ef-
     ficiency Calculation.   Department of Physics, Lehigh Univer-
     sity, Bethlehem, PA.  Technical Report No. 24,  1974.

15.   Agarwal, J.K., and B.Y.H.  Liu.  A Criterion for Accurate
     Aerosol Sampling in Calm Air.  To be published in Am. Ind.
     Hyg. Assoc. J.

16.   Davies,  C.N.   Sampling Aerosols with a Thin-Walled Tube.
     Presented at the 12th International Colloquium on Polluted
     Atmospheres,  Paris, May, 1976.

17.   Davies,  C.N.,  and M. Subari.  Inertia Effects in Sampling
     Aerosols.  In:  Proceedings: Advances in Particle Sampl-
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     Park, NC, 1979.

18.   Zebel, G.  Some Problems in the Sampling of Aerosols.  In:
     Recent Developments in Aerosol Science, D.T. Shaw, ed.
     Wiley, New York, 1978.   p.  167.

19.   Whitby,  K.T.,  A.B. Algren,  R.C. Jordan, and J.C. Annis.
     Evaluation of  Air Cleaners for Air Conditioning and Ventila-
     tion, Part I—Apparatus.  ASHAE Trans. 64:401,  1958.

20.   Berglund, R.N., and B.Y.H.  Liu.  Generation of Monodisperse
     Aerosol Standards.  Environ. Sci. Technol. 7:141, 1973.

                                408

-------
                   METRIC CONVERSION FACTORS
To convert from;

pounds, avoirdupois (Ib)
grains (gr)
grains/cubic foot
(gr/ft3)
inches (in.)
feet (ft)
feet/minute (ft/min)
cubic feet/minute
(ft3/min or cfm)
gallons (U.S.)   (gal.)
gallons (U.S.)/minute
(gal./min)
gallons/1000 cubic feet
(gal./lOOO ft3)
inches water gauge
(in. WG or H2O)
temperature °F
To;

kilograms (kg)
grams (g)
grams/cubic meter
(g/m3)
centimeters (cm)
meters (m)
meters/second  (m/s)
cubic meters/second
(m3/s)
liters
liters/second  (i/s)

liters/cubic meter
/ o /«. 3 \
millimeters of mercury
(mm Hg)
temperature °C
Multiply by;

0.454
0.0648
2.29

2.54
3.05
0.508

0.000472
3.79
0.0632

0.134

1.87
(°F-32) x 5/9
                               409

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                                TECHNICAL REPORT DATA
                         (Please read Instructions on the reverse before completing)
1. REPORT NO.
 EPA-600/9-80-004
                                                     3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
 Proceedings: Advances in Particle Sampling and
 Measurement  (Daytona Beach, FL, October 1979)
                                 5. REPORT DATE
                                  January 1980
                                 6, PERFORMING ORGANIZATION CODE
7. AUTHOR(S)

W.B.  Smith, Editor
                                 8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 Southern Research Institute
 2000 Ninth Avenue, South
 Birmingham, Alabama  35205
                                 10. PROGRAM ELEMENT NO.
                                 EHE624
                                 11. CONTRACT/GRANT NO.

                                 68-02-3118
 12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC  27711
                                 13. TYPE OF REPORT AND PERIOD COVERED
                                 Proceedings; 4-11/79
                                 14. SPONSORING AGENCY CODE
                                  EPA/600/13
15.SUPPLEMENTARYNOTESIERL_RTP project officer is D. Bruce Harris, Mail Drop 62,
 919/541-2557.
is. ABSTRACT Tne proceedings consist of 20 reports of research on equipment and tech-
 niques for sampling and characterizing particulate emissions  and other aerosols.
 The inhalable particle size range (up to 15 micrometers) is  emphasized, and the
 basis  for selecting this range as a standard is discussed. Novel or improved  equip-
 ment includes: virtual impactors; impactors for sampling high dust loadings;  an
 impactor/quartz-crystal-microbalance combination used to sample stratospheric
 aerosols; a tapered-element oscillating microbalance for monitoring particulate
 emissions and aerosols; an automated  piezoelectric microbalance for monitoring
 atmospheric aerosols; a hot-wire probe for measuring liquid droplets; sampling
 systems that are improvements on EPA Method 5  equipment for measuring mass
 emissions; and more efficient sampling probe inlets.  New or improved techniques
 include: measurement of aerodynamic  diameter by laser/doppler velocimetry of
 particles accelerated in a converging nozzle; automation of  diffusion-battery/conden-
 sation nucleus counter systems; sampling inhalable particles in fugitive aerosols;
 particle-size spectrometry for characterizing inhalation toxicity; computer extrapo-
 lation of particle-size ranges; and the  identification of impactor errors due to non-
 ideal behavior to particle  deposition in sampling probe nozzles.
17.
                             KEY WORDS AND DOCUMENT ANALYSIS
                DESCRIPTORS
                                         b.lDENTIFIERS/OPEN ENDED TERMS
                                                                  c.  COSATI Field/Group
 Pollution
 Dust
 Aerosols
 Measurement
 Sampling
 Properties
Analyzing
Pollution Control
Stationary Sources
Particulate
Characterizing
13B
11G
07D
14B
18. DISTRIBUTION STATEMENT
 Release to Public
                                         19. SECURITY CLASS (This Report)
                                          Unclassified
                                             21. NO. OF PAGES

                                               418
                     2O. SECURITY CLASS (Thispage)
                     Unclassified
                                             22. PRICE
EPA Form 2220-1 (9-73)
                                   410

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